U. S. DEPARTMENT or AGRiCULTURE, BUREAU OF ENTOMOLOGY,
Washington, D. (., Mfarch 16, 1909.
Sip.: I have the honor to transmit herewith manuscript of the first part of a bulletin of the technical series to be entitled "Contributions toward a Monograph of the Scolytid Beetles." This family of beetles includes some of the most important enemies of North American forests, as well as of crude forest products, and therefore must demand special attention in future systematic and economic investigations by this Bureau and by forest entomologists connected with other public institutions and private enterprises. It is necessary, as a foundation for such work, that the heretofore-described species should be accurately identified, that those new to science should be described, and that this information, together with other systematic data based on original research by this Bureau, should be made available in the form of contributions to a monograph. This work has been undertaken by Doctor Hopkins, of this Bureau, and the greater part of the collecting and working up of the material has been coinpleted. Delay in publication will be avoided, andl it is believed that the published results w%,ill be more useful in future systematic and economic investigation if the results relating to groups of species which have similar characters and characteristics and similar relations to given economic problems are published as parts of a bulletin rather than in one undivided publication. These technical parts are to be supplemented in a like manner by parts of a bulletin of the regular series, giving information of immediate practical imnportance to the forester andl owners and managers of private forests.
The first part of this bulletin is entitled "'The Genus Dendroctonus." It embodies the results of extensive systematic investigrations of the genus, carried on by Doctoir Hopkins during the past seventeen years, and is of especial interest andl importance from the fact that it deals with a small group of beetles wvAhich are the most destructive enemies of the principal coniferous forest trees of North America.
The discussions and illustrations relating to anatomical and technical details are necessary as a basis for the correct description,
III

IV LETTER OF TRANSMITTAL.

interpretation, and recognition of generic and specific characters, on which depends the future success of economic work on the scolytid beetles, and as aids in the preparation of technical and economic contributions to the monograph.
I recommend the publication of this paper as Part I of Technical Series, No. 17, of the Bureau of Entomology.
Respectfully, L. 0. HOWARD,
Chief of Bureau.
Hon. JAMES WILSON,
Secretary of Agriculture.

PREFACE 'TO 1117111 411N.

During the writer's investigations of extensive insect depred tit ions in the forests of West Virginia, from 1890 to 1902, he -vN-as forcibly impressed with the importance of the forest-insect problem in any future efforts toward the successful management of the forests of this country, and was thus led to give special attention to the subject. It was soon realized that among the principal groups of insect enemies of forest trees the scolytid bark and wood boring beetles must occupy first rank, both in economic importance and in systematic interest. Subsequent investigations in West Virginia, in connection with the work of the West Virginia Agricultural Experiment Station, and in all of the principal forest regions of the country, in connection with the work of the Bureau of Entomology, have served to confirm these first impressions.
In these, investigations special efforts have been made to acquire information on habits and seasonal history of the various species, and other facts relating to them, and to collect an abundance of material for systematic study-all to form a basis for conclusions in regard to the principal enemies of American forests and practical methods for their control.
The large amount of material has been pretty thoroughly worked over and identified, and synoptic tables and descriptions for the greater part have been completed for some time. Delay in publishing the results of the systematic part of the investigations has seemed necessary, in order that sufficient time might be given for the determination of taxonomic details as a basis for reliable conclusions in a comprehensive treatment of the group as a whole, but with increasing duties in the general work on forest insect investigations, and the more and more limited time available for systematic work, it is realized that these taxonomic studies can not be completed for many years.
To avoid further delay in the publication of data of immediate interest and importance, the writer has decided to postpone the discussion of the taxonomic and other subjects of a philosophical nature, required for a completed monograph, and for the present to issue separate contributions, each part to be restricted to one genus, or, at
V

VI THE SCOLYTID BEETLES.

most, to a few closely allied genera. These parts will include synoptic tables, the necessary revisions of old descriptions of species and genera, and descriptions of genera and species which appear to be new to science.
It is proposed to follow these technical contributions with parts of a bulletin in the regular series, to include the determined bionomic and economic facts.
A somewhat comprehensive treatment of the anatomical details, fully illustrated, is given in Part I of this technical bulletin in order that it may serve as a basis for reference and comparison in the subsequent treatment of the other genera and groups of the family.

LABELS AND RECORDS OF TYPE AND OTHER MATERIAL.

A single specimen (a female, if possible) is designated as the type of a described species by a printed red label ("Type No. U.S.N.M11."), with the type catalogue number of the U. S. National Museum written in the blank. When additional specimens are available, the type, with one other specimen representing the opposite sex, labeled S type" (or Y type") on red label, without type number, together with revision types a and other specimens showing range in variation, constitute the type series which is deposited in the type collection of the U. S. National Museum. Other paratypes and typical examples of revised descriptions, comprising one or more specimens of each species described, are marked with small red labels, and together with the duplicate collection of pinned, alcoholic, and biologic material, are kept in the reference collection of the Branch of Forest Insect Investigations, Bureau of Entomology, UT. S. Department of Agriculture.
All pinned1, alcoholic, and biologic material collected or received from correspondents are referred to in the field or laboratory records anItld )ears 1111111ber labels, each numIber referring to a consecutively n11iubered rc ec (df t ie observations h made at the time the specimens were collected o()r received.
Material collected by the writer (luring his connection with the West Virginia Agricultural Experiment Station between 1890 and 1902 is designated by) "llopk. W. Va.," number labels. Material collected b)y the writer luring his temporary employment on special explor;t ions all trips of investigation for the U. S. Department of Agriculture het weenll 1,9 and July, 1902, as well as that collected during the invest igt ions of forest insects subsequent to April, 1902, or received frni cTson(dents, is distinguished by a IlIopk. U. S." number label. In addition to the note number label each completely
The termii 'revisi+, t y!)e" is u d t d ignate the1 4p-in male and female, foI which a revised dhscrilti+n is bhaed.

PR E FA C E. VI1

labeled mounted specimen bears labels which supply the following data: Collector or correspondent, locality, collecting or rearing date, host, and sex. The numbered notes are permanently boun(1 in volumes of 1,000 numbers, each note relating to one or more species and to one or more specimens. The "ttopk. IV. Va." numbers begin with 1 and were limited in June, 1902, to 7,791, and in January, 1907, to 7,793. The "H~opk. U. S." numbers began with 1 in April, 1899, and will be limited to the period during which the writer is in charge of the Branch of Forest Insect Investigations in the Bureau of Entomology.
MATERIAL STUDIED.

Unless otherwise mentioned, the material which forms the basis of information and study, so far as it relates to matter in this bulletin. is that bearing the "Hopk. U. S." or "Hopk. W. Va." note numbers. The former is in the forest insect collection of the Bureau of Entomology, U. S. Department of Agriculture; the latter belongs to the collection of the West Virginia Agricultural Experiment Station, but at present is in charge of the author, and forms a distinct part of the forest insect collection of the Bureau of Entomology.

The writer desires to acknowledge the indispensable assistance and encouragement, during his earlier studies of the scolytid beetl'c

VIII THE SCOLYTID BEETLES.

(1890-94), rendered by Mr. E. A. Schwarz, of the U. S. National Museum, Oberforster W. Eichhoff, of Strasburg, Germany, MAr. W. H. F. Blandford, of London, England, and M. L. Villard, of Lyon, France. Messrs. Eichhoff and Schwarz especially were most kind and generous in furnishing identifications of species and in liberally losing aMnd donating specimens. Finally, the writer wishes to acknowledge the help of his associates and assistants during the prosecution of the work, and especially Mr. W. E. Rumsey, of the West Virginia Experiment Station, and the office and field force of the Branch of Forest Insect Investigations, in the Bureau of Entomology.
A.D. iH.

The active work on forest insects conducted 1y the West Virginiia Agricultural Experiment Station in 1890-1902, a nd by the Division and Bureau of Entomolo gy of the U. S. De partment of Aogriculture since 1899, has resulted in the accumulation of a mass of systematic and biological data on the principal described and undescribed insect enemies of forest trees and forest products of the United States. 'Whenever an attempt has been made, however, to work up the material relating to a given species, or group of species, it has been apparent that the publication of anything without first (describing the new species and revising the data in both the systematic andl economic literature would contribute to confusion rather than to advancement. Indeed, it becomes more and more evident that in order to give reliable information on applied entomology we must have at our command the knowledge gained by careful technical, or systematic, studies of the insects with which we have to deal. Therefore, when we find, as we do in many cases, that the published results of systematic work on a given genus or species are meager or otherwise unsatisfactory, it becomes necessary to revise and verify the descriptions and biological records, and to adjust the classification to meet the requirements of the newly discovered facts relating to the dlescrib~ed and undescribed species.
The genus Dendroctonus presents a striking example of the need of systematic study as a basis for economic investigate ion. It is both the most important group of insect enemies of the coniferous forest trees of North America and one of the most difficult for systematic study. Le Conte (1876) expressed the difficulty met with in a study of the species when he said in his later revision:
If I have failed to indicate more strongly the differences between these species, it is because they are not distinguishable by any prominent or definite characters; and the student who may have difficulty in identifying the species as here de~finled woulld have almost equal difficulty if the specimens in my collection were before him.

THE -,:CQLYTID BEETLES.

Cntil Nvithiji recent vezirs little procrress had been made toward the

different sta(yes, habits, etc., of D. frontalis, and larvT and habits of D. ter(,bra iis D. valens). In 1901 lie described D. pictaperda, iii all stages in connection witli an account of habits seasonal histonr etc., and referred to the type of D. ruf pcii nis (Kirby). In 1902 he described A poiiderosx in all states in connection with an account of liabits, seasonJ history, etc. In 1902, tinder" Some Notes on the Genus
he referred to a statistical method of determinill(r Dendroctonus, rnatural positions of the species, and (rave a list of described species and niimiscript nannies of tindeseribed species, as follows: D. pim( da 'MIS'S.1 1). arlzopi(,118 'Mss., 1). montleola MSS., D. ponderosa 11opk.
A keeni 'MSS., D. r1t ( -7
11S. I t fletche 'MSCS', D. piceaperda 11opk., D. d et--*
MSS.1 A californicus MSS., I). shoshone MSS., A mickhami AISS.,
and D. borcalls MSS. He res-tored 9. hrc -icomis Leo. ati(l D. puiictatiis Lee. from Dietz's synonymy, and recognized A obesus (Mann). In V)05 he described D. ps(,u(7otsugx ai-id D. mmiticola in collection Witli. accouilts of habits, seasonal history ete.

THE GENUS DENDROCTONUS. 5
SYNONYMY.
The following species were included, all but two of which were subsequently referred by Eichhoff (1864) to other genera:
Bostrichus ricans Kugelainn = Dendroctonus uicans (Kugelann).
(Type of genus.)
Scolytus terebrans Olivier= Dendroctonus terebrans (Olivier).
Dermestes piniperda Linnaus= fMyelophilus piniperda (Iinnoeus).
Hylurgus minor Hartig= 3.Melophilus niinor (IIartig).
Hylesinus minimus Fabricius= Carphoborus minintmus (Fabricius.)
REVISIONAL NOTES.
The generic characters mentioned by Erichson in the original description are recognized in the type and other species except that the maxillary palpi are not 4-jointed. The first or basal joint has a basal ring or outward curved basal margin for the attachment of the membrane connecting the joint with the palpiger. This might have been mistaken for the "very short first joint" referred to, but it is evident that this or any other structure does not represent such a basal joint. In the type species the first joint of the club is equal to the others, but ranges from shorter to longer in the other species.
Le Conte's added characters in his revision of 1868 and 1876 are generally correct, except that the antennal club is not always concave on one (external) side or anterior face, the sutures are more often curved than straight, and in some species only two sutures are visible on one side of the club. The prosternum is sometimes flat, the fifth joint of the tarsus is never longer than the others united, and the ventral segments are only approximately equal in length, the last one being usually as long as the two preceding combined.
Dietz (1890) called attention to the unreliability of the sutures and joints of the antennal club in dried specimens, and laid special stress on the value of the epistoma in distinguishing the species. It appears, however, that while the form of the epistoma is a good generic and subdivisional character, it is of little or no value in distinguishing the species.
The additional generic characters recognized by the writer will be found described under external and internal anatomy, and the characters distinguishing the major and minor divisions will be found in the synoptic tables.
REVISED DESCRIPTION OF GENUS.
ANATOMICAL.
The following discussion of anatomical details includes the imago, larva, and pupa, and is based primarily on the results of original dissections and anatomical investigations by the author during the

6 THE SCOLYTID BEETLES.

past eighteen years, and of those conducted by assistants under his immediate supervision during the past. three years.

abundance -of material at hand and because of the comparatively large size of the individuals of this species. Sufficient comparative studies have been made however of the other species of the (renus and of representatives of other genera of the family and suboi-ders to form a reliable basis for the interpretations and conclusions relating to the more important taxonomic characters and the significance of their modifications in the distinction of species, genera, etc.
Through the assistance of Mr. R. E. Snodgrass an extensive investigation has also been made of the thoracic segments of representatives of all of the principal orders of insects. The results have served as additional data and evidence on which to base conclusions in this paper, and will be utilized by Mr. Snodgrass as a basis for a more detailed discussion in a paper entitled "The Thorax of Insects and the Articulations of the Wings," to be published later. This will include a quite complete bibliography and references to the principal systems of nomenclature proposed or adopted by the leading authors, thus rendering it unnecessary to include' extensive bibliographic references in the present paper.
In all of this anatomical work the object of the author has been to acquire direct information on the facts as they exist in the subjects examined; such information to furnish a basis for the determination, naming, & description, and illustration of the anatomical elements as represented in the scolytid beetles, and at the same time to serve as a guide to the determination of further facts relating to insect anatomy in general.
The literature on insect anatomy has been utilized as a guide in securing additional information on the facts and principles involved, and with the idea of adopting such interpretations and nomenclature as appeared to conform more nearly to the facts and contribute to uniformity. No attempt is made to discuss the merits of opposing opinions or theories, or to prove or disprove them.
In this presentation of the results of independent investigation and discussion of the facts as interpreted by the author, it is hoped that something has been accomplished toward the advancement of information on the general subject of insect anatomy, and that its special reference to the anatomy of the scolytid beetles will make the future systematic study of this troublesome group less difficult and more accurate, and thus lead to the determination of bionomic, and economic data of immediate practical importance.
NOMENCLATURE.
There is yet much confusion in the literature and considerable difference of opinion among the best authorities in. regard to anatomical nomenclature as applied to the structure of insects in general and especially to representatives of different orders. There is

evidently much room for improvement in the line of uniformity in names and interpretations. In the present paper the writer has endeavored to adhere to the mrore generally accepted( names proposed II EA D

4. IAN

Front leg nIt lob

P1,scu tra
~1ciV('1 suttre ~'cuellum

>S1 a c/

PIC -Sq'tell2

FI.3-edotnsvlr-FAut aea set.a lua vcl;b pree a Orgna.

demand.te

10 THE SCOLYTID BEETLES.
ILLUSTRATIONS.
The figures are intended to be sufficiently complete to leave little to be added in the way of description, except to emphasize and elucidate some of the more important features, or to call attention to the variation within the genus or species.

EXTERNAL CHARACTERS OF THE IMAGO.
The structural details and general external anatomy and sculpture are shown in figures 1, 2, and 3. The principal characters peculiar to the genus are found in the large, prominent head, the epistomnal process (figs. 2, 3, 4, 6, 10) (referred to by Dietz as the median segment of the epistoma), the form of the antenna (figs. 11, 12, 13), the approximate or subcontiguous anterior coxm (fig. 2), and the strongly recurved hypopleural sutures 4, 5, and 6 of the abdominal sternites (fig. 25).
Length and relative proportionas.-The length of the imago ranges from 2.5 mm. in D. frontalis to 9 mm. in D. valens. There is considerable range in length within the limits of some of the species, while in others the length is more constant. The relative proportions of the width of the head, width and length of the prothorax, width and length of the elytra, or a composite of the ratios, serve as a taxonomic index for the classification of the species, and, together with other characters, serve to distinguish the major and minor divisions and, to a certain extent, the species. The progressive modification appears to be from a head nearly as broad as the pronotum and the latter as broad as the elytra, with the sides nearly parallel, to a head much narrower than the pronotum, the latter slightly narrower than the elytra, with the sides narrowed and constricted toward the head; also, from a slender, subelongate, to a. stout body.
(Color.-The color ranges from pale yellowish-red to brown and d(leep black, but is fairly constant in the matured individuals of a, species. The inmmnature individuals are always lighter, and some of those of the black species are redd(lish. In some species the head, l)rothorax, and ventral surface of the body are darker than the elytra, while in others little or no difference is noticeable.
estture.-The body is more or less clothed with short to long hairs, the presence or absence of which on different areas is of far more taxonomic significance than was at first recognized. Except in old rubbed specimens, the vestiture serves as one of the important characters distmguishing the major, as well as some of the minor, divisi0ns. See synol)is, Divisions I and II, sections al and a2 (Pl. I).
Sculpture.-Within the genus and also within each species there is considerable variation in the sculpture of the front, pronotum, and elytra. Nevertheless, such characters as the presence or absence

TIE GENUS DENDRO(TONUS. I1

of frGntal grooves and tubercles serve to distinguish some of the minor divisions of the genus, while the presence or absence of a posterior median impression in those species without a frontal groove is of considerable importance in distinguishing sone of the minor divisions. The relative size, density, and arrangement of the punctures of the pronotum, while variable within the species, is of considerable taxonomic value. The character of the rugosities of the interspaces and the punctures of the strive are also variable within the species and are of secondary value in distinguishing minor divisions. The sculpture of the elytral declivity is of special specific and sexual importance, and in some cases the characters are of value in distinguishing minor divisions.
TIlE HEAD.
The general characters and details of the external skeleton and appendages of the head are shown in figures 4, 5, and 6. It will be noted that the elements which in some other Coleoptera and other insects are more or less clearly defined are quite completely fused and obscured in this genus as in other rhynchophorous beetles. The labrum and clypeus are obsolete. The epistoma, or "post-clypeus," or "pre-front," as recognized by different authors, is not separated from the front by a line or suture, but is quite clearly defined, and the epistomal process is far more prominent than in other allied genera. The front is completely fused with the epicranium, which in turn is fused with the gene, the latter joined beneath with a single gular suture. Anterior to the gular suture there are three quite clearly defined sclerites, which may be designated as pregula, pregena, and hypostoma (fig. 5, E). By comparing the head of Dendroctonus with that of a carabid beetle, Pterostichus (fig. 7), and a typical curculionid beetle, Pissodes strobi (figs. 8, 9), the striking difference in structure and relative position of the corresponding elements and their extreme modification are at once apparent.
Labrum.-The labrum is not present as a distinct element, but may be represented by a part of the anterior margin of the epipharynx beneath the anterior median section of the epistoma (fig. 6, A).
Clypeus.-The clypeus is not represented unless it is by the produced anterior margin of the epistoma, and by the long epistomal bristles.
Epistoma (figs. 2, 3, 4, 5, 6, 7, 10, 40, B, D, E.)-The epistoma is apparently represented in both the larvoe and adults of all true mandibulate insects, but is more distinctly defined in some than in others. In some insects it is separated from the clypeus by a suture, line, or articulating membrane, while in others there is no evidence of separation or the clypeus is not represented. Its separation from the front is often defined by a line, impression, elevation, or otherwise, although sometimes it is so completely fused that the line of junction

12 THE SCOLYTID BEETLES.

is entirely obscured, as in Pterosh*chws. It serves the important function of a rigid bridge over the oral foramen and support for the. clYpeus, labrum, and epipharynx, and at its lateral angles provides the. necessary rigid support for the dorsal articulation of the nianAfandtNe

two lateral sections and is fringed anteriorly with thickly set, long bristles which completely cover the anterior median epistomal area.
~4 C

Hypostoma (fig. 5).--This, as here interpreted, is a ventral piece

or area which corresponds in general function to the epistoma in forming a ri gid ventral rim of the oral foramen for the seort of the
Fm.5edros;ooustveo coed, entra pet, a otar A, Lnabiprce; maxillary intdyle; 8, gular apodeme; u, oral foramen; v. occipital apodeme; ?v, postgular piece. (Original.)

two lateral sections and is fringed anteriorly with thickly set, long bristles which completely cover the anterior median epistomal area.
Hypostoma (fig. .5) .-This, as here interpreted, is a ventral piece or area which corresponds in general function to the epistoma in forming a rigid ventral rim of the oral foramen for the support of the

14 THE SCOLYTID BEETLES.

articulatory accessories of the labium and maxillm, and at the lateral 1,111cr -tipports the ventral articulations for the inandibless". It

seeim, to the writer that this part or area, -wheiiever sufficiently distiiia to be recognized, should be designated as the hypostoma, not

the epicranium. It is represented by a frontal area, however, which
not only in this genus but in other scolytids presents characters of special value in distinguishing major and ninor divisions, species, sexes, etc. The significance of frontal characters in this genus is defined in the synopses of adult and( secon(larv sexual characters and shown in the figures.
Antenna (figs. 1-6, 11-13).-The characters of the antennmw are
clearly shown in the figures. The scape, funiculus, and club are

nearly equal in length. The scape toward the apex is clavate-cylindrical to angular. The funiculus is 5-jointed and always slightly longer than the club. The first joint (or pedicel of some authors) is of the usual form and as long or longer, rarely shorter, than the second. The second joint is as long as the third, fourth, and fifth together, or slightly shorter in some species, and the second to fifth increase in width toward the club, which is broad, thickened toward the base and compressed toward the apex, and has three or four distinct segments, with two or three slightly to strongly curved

Epicranium.-The epicranium is not defined from the front or gena
by sutures or lines, but the area is quite clearly indicated by the

THE SCOLYTID BEETLES.

1111)0tltvr stirface Ztiid by the preseiice of the compound eye, which is sittiated mi the sl(le of the head near the base of the antenna e. The allteriol* (111d 4 the epicranial suture defines the anterior dorsal limit of the epic ranitt in, designated as the vertex, while the 0-ena is represented bv the. -ventral area between the eyes and the crular suture.. Tile epicranial suture is more distinct in some. species than in others.
P I !/(,,,;.-The eves vary from slightly oblong oval to oblong ovate and are obliquely placed in the anterior aL71e Of the epieranial area, just posterior to the base of the antenna e. The variation 'in forni within the genus and within the same species is shown in figures 1 to 6 and 1.5. There are about four hundred facets, which are small and densely placed.
Occijmt (figs. 4, 5).-The occiput is not earlyy defined, as it is in Pterostichus, but the posterior area of the cranium to the occipital foramen mav be designated as the occipital region or area.
occ pitalfi rain(;it (fig. 5).-The posterior opening in the head, or OcCipital foranien, is small as compared with the Ord foramen. The iiivagiii.ated w-all fornis a part and posterior support to the tontorium, an(l t1to (Im-sal apodeine is continuous with the epicrailial suture.
t;0-a.-The gula is not represented by a space delIned. by two lon(ritudinal stitures, as in most Coleoptera other than the iflivilchopliora. Pie (nilar apodenies are present (fig. 5 D), but the (rular Space is; im-a(rillatc(l, o that there is but a single, gular suture.
loittis there is a small sclerite 'niniediatelv
iula. N Amiro(
:tuten(w to tli(, (rtilar stittire (fio-s. 57 6) wliich is distinctly swpara (I ftom die (rulzi and (reii v by an inv tgiuated apodei-ne, laterally froin t1w pre(rean I)N- ..111 (IN-ident, external Iiiie, aii(l anteriorIv from flic l1\-,)()Sto111,1 b\- a ri(l(re wIlicli defines the alitcrior niargin. Ta t1w
lWetles this is e.xtelldcd it'll t1w pivgclia alld fol-Ills I lll0rV Or 1(11 di., t Hict giflar spacc (4 the rosirtini to a sinillar aiiterior space N\111(11 111)p wt, Ille o-c"I'lled (rtlial. lw illicitt( or stibillclittilli. 'I'llerefor", il 'Ilqw lr,-, HIA Hie terill inv(rilla "Imuld s(,lwe to (list t1il'S illi1wrt'llit clellient, whicli is also 1110111 Or Ic-'s rel)rvsented in Colc()I)tcl- l ()tll(,I. thall tll(, 1111ylichol)lm ra. (Colill),11V fi(rs. C) 1 8.)
61 1M.--rille (rell;l is ll()t defille(l hN- Illies btit it is RII)re-iented by Ille ventr'll ;Irca lwtwecli thc gtilal. sliture Illid the (1,1)icrallial area, ;I, 11c,(.1-11wd 1111dcr (,I)iCl"Mitill) '111d (rill,11. slittire.
-), *s t ( .11-111 area situI.- r 1 4 llst*ll(,t plet
.ftcd hetweell t1w b'Ise (4 t1le 'llitelill-v aild Hie pregula, boull(led P(r,11T1()1,IV bN- t1le (relial arva alid allterlor all(rle of flie ('Picrallillill, '111d h\, Hie ]IN-Im stollia.
Sllb/11(011111 di(rs. 5 ( ).-TIie subineiituin is represented 1)y it J)illd pl-1wess m. Illediall vxtellsloll Of Hie ll -postolna, 1111d is SUPP"Hild bV tw() -'t")[it braces risilig, t1le large trallsverse rostral '1p)(1cille belicatil Hic Imsteror alil(rle of Hie preo-11111.

THE GENUS DENDRO( TON 'S. 19

Labium proper (figs. 2, 5, A).-In Dendroctonus and other rhynchophorous beetles, the mentum, palpifer, glossy, an(I paraglossa, while more or less clearly indicated, are not represented as separate elements of the labium. Mentum: Thie minent ium a rt iculates with
the bifid submentum and completely surroun(ids the basal portion of the labrum, being subcylindrical, with the anterior ventral area strongly retuse. Palpifer: The palpifer is represented by the area between the ventral impression of the mentum and the row of palpiferal bristles which define the anterior limit of the mentum. Palpi: The labial palpi are distinct, 3-jointed, and as long as the mentum, or longer, with the first joint longer than the other two. or rarely equal. Ligula: The ligula
is situated between the palpi, is
tlhicklyset withlonglacinial teeth, and occupies the greater part ofk the dorsal area. It is evident
that this ligular area represents the glossed and paraglossa of other
insects, and that it is homologous with the galea and lacinia d
of the first maxilla.
Maxillx (figs. 2, 5, B, C).-The
maxille (fig. 5, B) have the characteristic form of those of all other rhynchophorous beetles and are
strikingly different from those of other Coleoptera. The form and relative proportions are shown in the figures. Cardo: The cardo is the stout basal section which
articulates with a condyle on FIG.10.-Dendroctonus:Epistomrnata. atol. D. ralthe maxillary process of the hy- ens; m to o,0. D. simplex: p to s. D. pseudotsugx.
th mxllrypocsso te.y (Original.)
postomal apodeme. Stipes: The (Original.)
stipes articulates with the cardo and, while it does not appear as a separate piece, it is represented by the posterior ventro-lateral and externo-lateral part of the median section of the maxilla. Palpifer, galea, subgalea, and lacinia: The palpifer is fused with the stipes and is represented by the anterior part of the median section (fig. 5). The palpifer and stipes are also fused with the subgalea on the exto-lateral area, but on the interno-lateral area the line separating the palpifer from the subgalea is distinct, as is also the suture between the latter and the lacinia and galea, which are fused, the latter being represented by a narrow chitinous margin next to the palpus and palpifer. The lacinia is armed on the inner edge with stout lacinial teeth. The length of the base of the subgalea from the apex
1-34440-11- 3

12 1 0 THE SCOLYTID BEETLES.

to the po-sterior angle is usually greater than the lencrth of the palpifer r115 r-)
Z111d stripes, but is sometin-ws equal mid rzirely shorter. The ventral

articulation witli the epist.onla, i 4 adapted to Illect its
veral requirements. The trocli11,1111, Mechanism of the
-irticulating con(IN-l-, ;ind fosszi are i11Listrat(',' in -figure 14.: fliat of ilr, dorsal e,(-,)ndy1,- zippers to be cornnion to other rlivnellophorous
I-)ut app;1J'('l1t1:\- not reprv (,iite(] in otlier Colooptera, including t!iose witli siinilir bnrk and wood boring babies. The -NI-entral articulation also zippers to be different from that in otheq- Coleopt""ra, but to a, degree. A (lefi'lited comparative study of the
mandibles mav reveal specific characters, but as a rule sliell chzintcters, are unsati.s.fzictot- from the fact that in compat-isons the man(lible, must be viewed from exactly the same position to avoid error in conclusions.

THE SCOLYTID BEETLES.

THE THORAX.

The thorax, as usual, consists of three dishiiet segments. The prothorax freely articulates with the mesothorax, but the pleurites Mid termites of the mesothorax and metathorax fare rigidly connected. The combined length of the ventral areas of the. three thoracic 6egnients is slightly greater than that of the ventral area of fhe J)domiiial segnients, while the combined Iencrth of the dorsal

beyond the ventral margin of the same segments, while the posterior dorsal margin of the pronotumn and the anterior dorsal margin of the mesonotum are not produced beyond
the corresponding sternal margin. 4
DIVISIONS Of THE THORACIC SEGMENT. 0 (
The divisions and other characters 2
peculiar to the thoracic segments of a 0 22a 239
scolytid beetle are shown in figures 16, ,0 2,b 23,
17, 18, 19, and 20. 2.1( 23i
It will be noted that while the usual '3
divisions or sclerites are quite clearly de- 02 6 ) C 7 23i fined in the metathorax, corresponding ( 23h
divisions are less distinct in the mesothorax, and are obsolete or completely fused C 4
in the prothorax. The taxonomic signifi- m ( .1( >
cance of this wide range in the modifica- FI. 15.-Dedroctonus: Eyes. 1,breition of similar parts or areas in the three comis; 2, barberi; 5, arizonicus; 8, apthoracic segments of the same insect is proximatus; 10, !ou, ponderosa; 12,
simplex; 13, pseudotsuge; 14, piceaperda;
realized when we compare these parts 15, ia, engelmanni; ?0, punctatus; 22,
with corresponding segments in repre- 22a, b, c, terebrans; 2 23a, b, c, d, e .
sentative species of other families, sub- g, h, ,k, vals. (Original.)
orders, and orders of insects. It will be seen that each segment has characters peculiar to the order or minor group to which the species .aa. .belongs, and that in like
manner the combined
characters of any two
A ............. or all three in the same
insect present many feah tures peculiar to the groups,
"B"the suborder, family, genus, or species represented.
k It is also significant of
o the influence of a domie \, nt principle or plan of
b ,"structure and order of modDE D ification that one or more
FIG. 16.-Dendroctonus valens: Areas of pronotum. A, an- thoracic segments of practerior area; B, median area; C, posterior area; D, lateral area; E, dorsal area; a, anterior angle; aa, anterior margin; tically any insect examined b, posterior angle; d, basal margin; e, posterior declivity; will show certain divisions f, anterior section of lateral area; g, anterior section of dorsal area; h, median section of lateral area; i, median section of more or less clearly defined, dorsal area; j, posterior section of lateral area; k, posterior section of dorsal area; 1, posterior margin or vertex, which are common to all (Original.) other insects, and that
when we compare the segments of different stages of insects of all orders, we find that a composite segment would represent a system of four longitudinal and four transverse divisions. The longitudinal

connected with the anatomical problem, it was this state of confusion which led the writer to make a study of the subject in or(er to (Vt ermine the facts and principles involved and to establish a basis f()r his future systematic andI economic work on the sco-lyti(d and oli(er beetles.
There appear to be two opposing ideas regarding the origin adl(t evolution of the primary and secondary elements of the insect segment. One involves the principle of reduction of several primllitive segments into one, on the theory that the transverse divisions r1present mnodificat ions of several primitive segments. The othcr involIves the principle of complex modification from a simple undivide(d primitive segment into many primary and secondary divisions, on t he theory that this has been brought about more or less independent through the influence of the requirements of function to meet the demands of peculiar life activity in different forms or species, and that this plan of modification has been controlled and limited )y the fundamental plan of structure in the hexapodal type of organism, and by the principle of relative proportions and correlation of parts so as to conform to the general modification of the entire body in the evolution of the species.
The writer does not deem it advisable, in this connection, to discuss the relative merits of these theories or any of the other theories advanced by different authors. Ile is inclined to believe that while it is important to utilize any good evidence relating to the probable origin and homology of parts, it is more important for present needs to deal with the facts as they are found in existing forms and stag(,s and to so name and define the major and minor divisions or enemts of the segment that they may be readily recognized and utilized in any comparative study of their modification and in the description and identification of species, genera, and larger groups. Therefore the writer's interpretation of the recognizable elements in the thoracic segments of Dedroctonus does not involve any theory of origin or evolution, but is based on the recognition of a dominant tendency in the insect segment to represent a system of four longitudinal and four transverse divisions, any one or all of which may or may not be clearly represented in one or more segments of the same insect.
With this conception of a prevailing principle as a guide to the location of the possible primary and secondary divisions of the anatomical elements as they are indicated in any given segment, and to the recognition of the possible range of modification and distinction as manifested in the different segments of the same insect or in the corresponding segment of different insects, many of the difficulties and confusing factors relating to the proper defiition of parts and application of names are eliminated.

26 THE SCOLYTID BEETLES.

In the following discussion of the thoracic segments reference is made to the named parts as represented or not represented, as the case may be, rather than to say that they are present or not present, because in some cases where they are not defined on the external surface they may be indicated by apodemes or lines on the inner surface of the body wall, while in other cases their position or relative areas are indicated only by some character of surface sculpture or vestiture.
In the adult Dendroctonus there is a wide range of difference in the representation of parts in the prothorax, mesothorax, and metathorax. In the pupa there is a similar but not so marked difference between the three thoracic segments, the divisions being less evident in the mesothorax and metathorax than in the adult, but in the abdominal tergites the divisions are quite plainly indicated. In the larva there is not only less difference in the three thoracic segments, but these are only slightly different from the first to seventh abdominal segments. In the thoracic segments the prescutal and scutellar divisions are clearly represented, with evidence of the scutal division on the sides. The sternal and sternellar divisions are also clearly represented, with evidences of the presternal and poststernellar divisions in the prosternum, and the latter clearly defined in the mesosternum and metasternum. The pleurites are also represented by pleural lobes. In the abdominal tergites 1 to 6 the prescutal, scutal, and scutellar divisions are clearly represented and the sternal, sternellar, and poststernellar divisions are in like manner represented in abdominal sternites 1 to 8, inclusive. Whether or not these divisions or lobes are homologous with (divisions occupying relatively the same positions in the pupa and adult may be a subject for difference of opinion, but the names here applied to what appear to be corresponding parts should serve as a reliable guide to their recognition and accurate definition and description in comparative studies and identification of species.
ELEMENTS OF 'rTE ADULT THORAX.
The primary and secondary elements as represented in the thoracic segments of an adult Delroctonlus beetle are shown in the figures and(l are interpreted, named(l, and( described as follows: a TUE PRIOTIIOLtHAX.
In this genus, as in rhynchophorous beetles generally, the tergal, pleural, and sternal areas are fused into a continuous band. The a Notui/ anid teruim. While the names notumi and tergum are synonymous, the former hLs been applied more speciically to the dorsal division of the prothorax, espe ially in beetles, and is here utilized in that sense. The name tergum is here Wued to designate the dorsal areas of the mesothorax, metathorax, and abdomen, on warounlt of the use of the term termite to designate a subdivision.

TIE GENIUS DENIDROCT(ONUS. .)7

primary and secondary divisions are not indicate(l by lines or sutures, but the corresponding areas are suggested by peculiar characters of sculpture and vestiture, which are of more or less taxonomic importance, and thus may be arbitrarily indicated, as in figures 16 and 17, to serve as guides to the location of characters in comparative study and description.
Pronotum.-The pronotum is the dorsal or tergal area of the prothorax, as defined by the anterior, posterior, and lateral margins. There is considerable specific variation in its structure, sculpture, and relative proportions. It ranges from about one-fourth to about onethird broader than long, with about the same range of difference in the width of the posterior and anterior areas. In some species the lateral margins are nearly parallel, while in others they are distinctly convergent and constricted anteriorly. The anterior margin is broadly sinuate, while the vertex or dorsal margin of the posterior declivity is bisinuate. The anterior area is broadly transversely impressed, except in the females of some species, where the median section of the area is transversely elevated. The posterior declivity, which perhaps represents the postscutellum, is more distinctly exposed and defined in this genus than it is in allied genera and is therefore an important character of generic distinction. The pleural and sternal areas are indicated in figure 17.
Episternal area.-The episternal area is limited dorsally by the lateral margins of the notum, ventrally by the smooth exocoxal area, posteriorly by the epimeral area, and anteriorly by a preepisternal impression or in some species by a ridge. The sculpture of this area is quite variable and in some species furnishes characters of considerable value.
Epimeral area.-The epimeral area is represented by a flattened, smooth space situated between the roughened episternal area and the posterior margin of the prothorax and between the coxve and the basal angle of the notal area.
Sternal area.-The entire sternal area between the anterior and basal margins is largely occupied by the coxal cavities, which are separated by the very narrow intercoxal or sternellar piece. The elevated anterior margin evidently represents the presternum, while the sternum is quite clearly defined by a nearly vertical flat to concave space between the presternum and the coxve, the lateral limit being indicated by the smooth, shiny exocoxal area between the coxaw and the episternal area. The sternum proper is quite variable, ranging from concave, smooth,'and shiny, without trace of a median longitudinal line to nearly flat, roughened, or with a median subcarinate line; but apparently none of these minor characters is sufficiently constant, even within the same species, to be of much taxonomic value.

28 THE SCOLYTID BEETLES.

Post.oteri?,611ar area-The post st ei-iiellar area is well defined and serves to complete1v inclose the coxal cavity. It has been referred to as the epiinen)ii, but siiice the eplineral is so clearly defined as a lateral area, IL apluars to more correctly rel)reseiit the poststernellum, which in the mesosterimm and inetasternuin is not evident, or is RIO(lifie(I to (i(-(-()iiimo(.Iat(, the large coxal cavitiVs.

,rl1E NtESOTHORAX.

The mesothomx (figs. 18, 19) is short and partially hidden front view by the prothorax, whiell. covers the anterior third of the sterna, pleuntes, and termites, \N-Iiile the base of the el tra covers

I T I I
I I x I I I I I I v I L, I I I I I
v t I( I t c rn 1 1.1 11
I )sIph r(I qIlt (I Thc )st I I rtl (ZI I I I I 1- F( n I I t c
I I I v a ti Ila I I( )II Q, I,( dd I w I I( ,I I le Sc I I I v I I Ill '111d I)v t ll(- I I I.:l I I IA 11 11 IN ( I V I I I )v I I I I t t a c I I I I I I I I (d, t he --wilt al 11111,-Whl Ill, 1110 itild
tho c()IIIwctI()II (d I lit, arm \\ It It t Iw IIIN-,w-rIlIIt el I PI1I*;I11*Ill,,I .
I-A I A.
Thc (,I)it ('11111111 111-ccp-P-1 1, M find ),I ruill, are
her ( )(-(-If pv 11) "11,0:1 (rl,("Il cr t IIIIII tim f ( )f t lit,
,t c I'li'l I ,I It( t I N, (rl,(,,l t (,I, t 11,111 111,11 )f I 11(, t (, p r l 1.
Pr( ( pistf r/i I/, w prec I )I-A erlill I I I wcu pw-- I Ill' tre 14 ill f I I I t
I ,, I I I v I I'S( I I I I PIVII-NP )II "Ilid F- I I I I i I I I I Will T] I e I I I ri 1, 1 1 1 :1 V7-1*111 .1 I'S t w n rI I I III(-I I 'I 1111111 ill I
I I I v I I I I d I I I-,I nlld [.- IM H11 IV PIVI- 11111 ("I I
)I I le r de( q )t ern -,I Ic I I I I I I I ( I I C ]c Ill( ](,Ill 1,1 I F;l I id ;l.. I,
.t SI I 1-pl-i ,4' Ip r t 11 1:11 it i no 0 re prc c ill 1 111 [p,
t 11 w-1 0 11, 11' N
N'PI v Illm l, fiell "it I I [.,I (. f f r 'llid fit 11cl it l I I
1*11 11 IN F( q d, ()I(,( Ip tc I-,I fro )I I 1 111 d ) ,(- I I ro "w ( I
CIC I I r( 1( 111 I)e if I // e )cIf
t I I t r ] I' I I I ;t I*t ri I I I I I I] I I I I I I I I I I I I I I I I. I I I ri N- 1, ; ) I f
I I I I I w I P I I I c. a
f I lic Imst ,(.l I t clia r all( I -;( I I clin r I ren s of t I w I'( I I I I I I I I I I I I I
I lit'r Il p )N\-(, 1.1*11 1 fill ISc Iv c ( )l I I I t I I I I I I I I I 1 11 T I I
I I I csi. I I":1 c I c Pi F", le I I I I I I I t v( I I I I I I I I I I
alld the Sternal area and i c()vered h.\ t hf. c1m.l.,m ial :1 4 11(,
Prot Ilorax.
Ww 'rlc ".4lender pl-.1tv sit 11"I I ed ill f 1.()Ilt ( 4 1111, 1 I'll I if
the preepisternal process appell's to (IM1,01.1wild \\ it It I lit, chivicle
( lisk of t he I net a ple i i ri i i I I I t I...; c( milec I v I If -(r"Illient I ( ) I Ill. It ("ll I
of t Ile e IV t rn it 11 1 t s nill"cle I I t t I I c I I I I I I'm II ment .I rv : I I I t 4
COXIII plece. Both the preepisternal process 'alid tile chivicle Id"ite,

30 THE SCOLYTID BEETLES.

as here defined, are probably modifications of the episternal paraptera of Audouin.
Episternumn.-The episternum is the clearly defined, large, exposed triangular pleurite situated between the posterior margin of the preepisternumi and the epimerum, with the dorsal angle dilated, prod(uced, and flexed ventrally at the apex and with the apex of the epimerum and preepisternal process forming the pleural claviculus with its clavicle and coracoidal condyle for the articulation of the elytra. The posterior angle of the episternum is acute, and the
suture between it and the sternum is obliquely sinuate. The episternal impression is clearly defined by the elevated posterior margin of the preepisternum, and is usually covered by the posterior margin of the prothorax.
Epimerum.-The epimerum is exposed at its posterior ventral
half and has its posterior margin fused with the metasternum and minetepisternum and the produced anterior dorsal angle with its coracoidal condyle is covered by the episternum.
Postepimerum.-The postepimerum is represented by a small declivous area beneath the posterior dorsal angle, where it covers the metathoracic spiracle.
MESOSTERNA.
Prestern u m (fig. 18).-The presternum is quite clearly represented by the narrow, slightly elevated, anterior margin joined directly with the anterior ventral angle of the preepisternum.
Sternum.-The sternum is short, flat, and subdeclivous, with the posterior angle (exocoxal piece).extending around the coxal cavity to its junction.with the anterior angle of the metasternum.
Sternellar area.-The sternellar area appears to be represented by the elevated and( rather broad intercoxal piece, while the poststernellum is apparently represented b1y a poststernellar piece.
THIE MET \THORAX.
METATE WGUM.
Fromn a systematic anl taxonomic point of view, the metatergum is )by far the most important and interesting part of the thorax of beetles. We find in it not only evidence of the four transverse (livislions, but exampl)les of the possible extremes in modification to 111eet th 1equireeifltS of wing articulation and wing Imotion.
Tra ers suturcs.-By a com01111arison of the imetater ni of representative s of different orders of insects and of the larv, pupe, and adults of some insects, as in Dendroctonu8, we find that the prevailing pI)rinlciple of division involves three transverse external lines, sutures, or impressions, and three corresponding entothoracic ridges, apodenies, or invaginated ectodermi, which define more or less clearly the four divisions, viz prescutum scutuill, scutellum, and postscu-

THE GENUS DENDROC'TON U'S. 31

tellurn. We also find( that these transverse sutures are su)ject to great variation in position, contour, character af urlfae, mnanifestat.

tions, etc., to correspond with the enormous range of modification to which one or all four of the transverse divisions are subject. These
external evidences of separation of Iarts are here referred to as sutures.,

riorly by the oblique initiated Iiiie (J flie Illediall stiture allot the lateral section of the posterior ridge.
Scutellum.-The scutelltun is represcifled ex 4,v 1*11 "Illy by Ole '11-ca posterior to the oblique line of the niedillti stittirv .111d by flie S111d'dera] and lateral rid(re. which termijiates iii flic, setitc1lat- is is
indicated by the, character of the etitotet-crimi ltii(l hy CMI I
with the less modified setitelhir divisionn iii ()fliei- iiisects. 'I"lle median longitudinal groove appezirs, to rep'rese,-lit, the iIiedlian proditccd section of the scutellum rather flian Zt part of the sclit'Itin or In-em"I'ltuml as indicated by the character ol' tJie entoter(ni III "I'lld t1le Widelyseparated apode'mes of the mediall 'tltllre w1lic1i c Ielld to -1,11d, Join Apterior apodrmr
c in 1) ra it n it s a Pea
Aii(crio'* lobe
Prc8cu tat di,, C
ill-csoutal lobe
-A

Lalciwl mo),( 'natiw)
ISCU tu M_7
\1 M4.
'-'-IRIapleural hook,

FIG. 21.-Dendroctonus valens: Metatergum, iimer aspect. a, Lateral arTU of band; cscapulararticulation; d, posterior angle of prescuttim; e, posteriorarin ofpostilmi ,,m: : v po- terior apodeme; g, anterior disk; h, posterior margin Of SCU1011UT11; X, ventral Nvall of (Original.)
with the anterior apodelne (fig. 21), thus definhicr a large itie'dian triancrular area NN-Lich is evident1v scutellar.
Postscutellunt. -The postsetiteduni is the exposed dorsal tand lateral area between the clearty defined posterior suture. alid the line of attachment of the first abdoiiiinal. termite. It is 1'rinly c()Tlliected wilLh. the, scutelluni toward each side at a pohit iu.,-ar the ()f the
oblique apodenie of the middle stature, otherwise the collection is membranous. The anterior (ingles suppoi t the iiietti"letiral hooks (ficr. 20 E u),which fit into a f old in the dorsal iriargin of flie postepizn I
merum (fig. 20, p).
Postphragma.-The postpbragma is tin invagination of the posterior section of the postscutellum and, with the prodticed posterior disks and arms, serves as important postel'i(")r attachments for the longitudinal, tergal, and oblique scutal muscles.

34 THE SCOLYTID BEETLES.
METAPLEtU RA.

The metapleurum is well developed and distinctly represented by the two longitudinal sclerites, episternum and epimerum (figs. 3, 20), with their anterior dorsal angles greatly produced to form the plural clavicula with its clavicle and coracoidal processes.
Pleural suture and apodeme.-The pleural suture marks the line of division between the episternum and epimerum, and extends from the dorsal angle of the coxe to the apex of the pleural clavicula and between the clavicle and coracoidal process. That this is the true pleural suture is indicated by the corresponding prominent pleural apodeme. It is also quite evident that the episternum corresponds to the hypopleurites and the epimerum to the epipleurites of the abdominal segments (figs. 3, 22).
Episternum.-The episternum is exposed when the elytra are
closed (fig. 2). The suture between it and the sternum is distinct and nearly straight, with the anterior end curved toward the coxa. The posterior ventral angle is oblique and joins the posterior dorsal angle of the sternum; from here the posterior margin is oblique to its acute junction with the epimerum and the dorsal angle of the coxal cavity. From here the dorsal margin is acutely elevated to fit into the anterior lateral groove of the elytron, and is nearly parallel with the ventral margin to the preepisternum.
Preepisternum.-The preepisternum appears to be represented by the narrow declivous anterior section of the episternum connected with the anterior basal area of the pleural clavicula and is apparently involved in the formation of the clavicle process. The clavicle disk evid(lently represents one or both of the paraptera of certain other insects and belongs to the prepleura. It is situated immediately anterior to the preepisternum. It is large, prominent, and partially exposed, and is connected by a chitinous tendon to the side of the clavicle process. This disk supports the set of large clavicular or sterno-pleural muscles, the opposite ends of which are attached to the sternum and sternellum.11.
En mernm.-The epimerum is situated between the pleural suture and(1 the tergumI. With the exception of the extreme posterior vent ra angle of the postepimerum it is covered by the elytra. The anterior dorsal ang11 le is strongly produced to form the coracoid pr()oCs. T1 velntral area is chit inou1s an(l is joined( to lthe episternui by the I)pleural utu(, while the (orsal a1rea is subminembranous t< Ilelbrous t its junction with thle base of the wing membrane.
Ie)().Inrin. -T I steri(or ventral angle and posterior lateral sdct 1l e)Ipreseint the pI)ost)iierull, as is i(icated by its articulator jIllti( 1ln with lthe )oststernellui (fig. 20, p). The posterPi L

THE GENUS DENDROCTONUS. 35

ventral angle -or ventral section of the postepimerum, which might be mistaken for a postepisternum, is indicated by the pleural apo(deme and pleural suture which here join the dorsal angle of the coxa. It is not impossible, however, that this plate may represent a combined postepisternum and postepimerum.

M ETASTERNA.

The metasterna (figs. 2, 3) form a broad rectangular plate separated into two lateral sections by a median longitudinal line. The presternum and poststernellum are not represented by external parts.

Sternum.-The sternum is evidently represented by the large continuous area between the mesocoxe and the small median plate and the slightly acclivous area anterior to the metacoxa.

Sternellum.-The sternellum is evidently represented by the posterior median plate and the posterior acclivous areas (fig. 2, a). The relation of the latter to the sternellar area is indicated by the attachment of the posterior pair of clavicular muscles.

THE ABDOMEN.
The abdominal terga, pleura, and sterna, and their relative proportions, are shown in figures 1-3 and 22-25.

134440-11- 4

36 THE SCOLYT1D BEETLES.
ABDOMINALTERGITES.

The elorlit ab(lominal termites tire normally covered by the elytra. The apparent dilrerence in the relative proportions, as indicated by fitllures )) and 22, is (lue to the flexiWe intersecrinental iiienibrane and the fact that fig-ure, 20 is from a balsani ia-iount. The intecrument of I to G, inclusive, is more or less menibranous, while that of 7 and 81 witli the exception of the finely sulc-,,tte membranous lobes of 7, is
(Adthious. In the feniale, S is Cover('d by 7) zind fornis the so-called

The Inedian area is triangular in form andl c()vere(d with bristles and hairs rising from variously formed bases. On its face and sometimes on the posterior area there are a few irregularly arranged truncate tubercles (I), m), each bearing a short, stiff bristle. These may possibly function as sense organs.
The membranous lobes are subovate, finely sulcate, and thickly clothed with reclining microscopic spines (o). Ihe exnct funci)ni of these lobes is not known to the writer. Tergites 4, 5, and G have similar lobes. The other (lorsal and ventral chlaract(rs' are llmad(e sufficiently clear in D1) and E.

Tergite 8 (A, B) is the pygidium. This, in the male, is always ,, Io trgte7 haitlarger and more exposed beyond the margnoftrgt, ta i h
female. The relative p~roporions, as compared with 7, and the dorsal and ventral characters are clearly shown in A and B. The lateral arms serve as attachments for pleural muscles and articulating membrane and ligaments. In C the abdominal sternite is added to show its relative position and proportions.
Pygal tergites of the female.-The p~ygal tergites of the female are shown in figure 24, A, B, C, D, E, F.
Tergite 7 (propygidium) is much more simple in structural details in the female than in the male, and tergite 8 (pygidtium) is also more simple a-nd shorter, being almost or e tirely covered by 7 when in

normal position.
The characters of sternite 8 are shown in D, the most important of which is the median membranous area.
it reltiv poiinadpootos

38 THE SCOLYTID BEETLES,
ABDOMIN-AL PLEURITES5.
At tlie lateral cii(Is of the abdonunal tero-ites and sternites there OlVe Well-(.1efille(I area-s (figs. '31 22; 2-5), which may be designated -as pleurites. Those Situated immediately above the pleural suture and beariiig the spiracles may be referred to as eppleirites, '\N-Ilile those of tile sternifes w1ileh are, immediately below the pletinal suture may be (lesicrnated as hypoploam4tcs; both series are well defined in Dc it drocto Ims.
III a lateral view (fig. 3) seven epipletirites and five hypopleu rites are clearly defined, with the, eighth epipleurite, and the secolid IIVpopleurite indicated, and when the Adomen is, removed both the finst an(I Second of tile latter series are quite distinct.

indicated in the wall of the coxal avit v. Stornites i4, 5, and 6 are nearly of equal length, while sternite 7 is nearly as long as 5 and 6 together, with the posterior margin broadIly curved and forming the apex of the exposed series. Sternite 8 (figs. 23, C', and 24, ) i entirely covered by 7, and is represented in the male by a narrow chitinous rim below the anal openillng, while in the female the median section of this sternite is minembranous.
Suture 3, between sternites 3 and 4, is the first visible suture, and( is rigid and straight throughout, while sutures 4, 5. and 6 are slightly flexible and are strongly recurve1 toward and between the hypopleurites, thus presenting an important generic character.
SPIRACLES.
There are 9 well-developed spiracles, 2 thoraci and 7 abdominal, with the rudiments of a tenth. The large mesotlioracic spiracle is located in the intersegmental membrane between the 1)pro)tlhorx and mesothorax, and( lies between the p)reepisternal process anl(i the anterior ventral angle of the preepisternlum. It overlaps tile anterior margin of the latter for half its length, but is completely covered( an(d obscured by the epimeral area of the ) prothorax. The metathoracic spiracle is situated in the intersegmental membrane between the metathorax and mesothorax, and concealed beneath the dorsal margin of the rnesepimerum. The abdominal spiracles 1-7 are conspicuous: 1 is very large and situated in the epipleurite just posterior to the pleural hook of the metapostscutellum; 2-7 are situated in their respective epipleurites, as shown in figures 3, 22, 23, and 24. while
8 is evident, but rudimentary.
TIHE LEGS.

The structures and characters of the parts of the legs are so well illustrated in the figures (figs. 3, 26-29) that they (to not require detailed description. The procoxwe and mesocoxa are large, globose, and prominent, the former subcontiguous and the latter widely separated by the elevated intercoxal or sternellar piece, while the metacoxe are oblong, oval, and separated by the process of the third abdominal sternite. There is no striking difference in the anterior, middle, and posterior trochanters, femora, tibiwe. and tarsi. The trochanters are small: the femora are moderately stout, and'each is as long as its tibia, which is dilated toward the apex and armed on its outer lateral margin with stout teeth. The anterior dorsal area has a distinct tarsal groove for the retractile tarsus, as shown in figures 26 to 29. The tarsi are each more than half as long as their tibie, and have five joints: joint 1 is always longer than 2. but never as long as 2 and 3 together; 3 is distinctly bilobed, the

40 THE 6COLYTID BEETLES.

lobe,- -4ightiv longer than j(,,)iilt 4; joint 5 from tip of lobes of 3 is never as lon(r as the others (t to 3) together, but sometline.,; shorter tkan I and rarel v oqual to 2 and 3. In the niales this joint is often
1011(yvi. t1lan ill the felliale.
TIte trochlear articulzitioti of flie tibill with the tarsus is showil
figure 26, ill which the (41wi-moreimportaut characters are -]I
sli(m aild
IM111(ld.
(d
TIIE

4,4 N ()t\\-i I I 1,,4 z I I) d i no, t I It, A-, Is t
1111oullt of publi'-died d;lta
ontheNN-i, -,- ts, t he re
Yet 11111ch difycrelice of
()pinion amom 111(r
the 1(,(idi
F Z--) rll
authors in regard to some of the detailS7 11,111d much confusion exist.,.;, (Itiv to different, interpi of
P
the llmilolw),W-, of the (,I(,A a h E
melit'-; of the wilw- nild its ao iculatol-.N acce,- ()I-*v,- A det'llied ill -est"(rotolt 11.1s bccii made of tho ba ,d Iffe(IS Of the (d rep--A
rvsentat ives I I ffe re I I I
G 0i'der, of ill'-wos, to deterF1 2,,- 1), wlrocl o n I/ < I (I li /',.- Tiiia mil m ilic f,.I(.t,, reloting to the fulld:1111clitat plall4devel()plitclil 111(1 modificiltiOll, ipi(;tl foul i, c, 1,,r :d 1,r-tve: d.
:(,oili: ,jm (r,d h, alld ille SVI-'teill (d, o r(ralli1,1 rrd If),-:t of lem M'-. ()It I' Ille (Acillen ts Z1,
k1pre:-'elli ed in form :if-!i: h:iwnt ol flev)r q. h)
OclOtill-I v
I ]w illolv "'clict"111Y w-cepled 11milellchilurc 11,1s been adopted, it
1(4 1 Ilece -;-- ,11. to '111d 111(wc dchllllel. defille the lpplic,111011
(J >mllc id ille (Jd 11,11lic-, ;tild to illirmilict, s(mle ll(,N\ mics to 11;Itc the elcllwill,- 11cl-cl(4mv V fillede.
Altm,11111(lits (/ Id /r/ /,c Oat imix. There 'Ire cerl'[111 clemcllt.- ill Ole ,t 1-11 c I I I tv I I I vc I I ; I I ) 1.- I I I t I I (- I I I I Ivilts, all( 'i rt I c ( I I a t I M I C( )111111( )11 0 Illc (d, d l 111.- ccts, but \\ i t I I i I I ( I c f i I I c( I I I I I t s a 11( 1 a cc( ) I.( I I I 10' t a
I I I I c N-st c I I I Ill( )(11 fl(.,l i D m s, ;lddil w il", '111( 1 I-educt iolis occu r. "111cl-cf(we 111c m. 'thsclicc of it givell Clemej.1t, should be
detected ill ;lm 1*1)1.111 (4 \\-I*II()-

VESTRA-1,
Fmi. 2-,.-1)todroowoi.,. Left (,or.
(Ori-iliaj.)
pleurum, and by ligaments and tendons to tergal and pleural processes and muscle disks. The pleffra.1 processes are the clavicle and
coracoid processes, which togetlier form the pleural clavicula. Th e
tergal processes are the prescutal., scutellar, and postscutellar.
Rement.- of wing ii/ol"*01t.-The elements of wing motion are the clavicular disk and clavicular muscle, pleural disk and pleural muscle, flexor and flexor muscles, prescutal disk and muscle,,;, anterior presCUtal lobe and anterior sternotergal muscles, postei-ioi- prescutal lobe and posterior sternotergal muscles, scutal lobe and scutal muscles,

4 2) THE SCOLYTID BEETLES.

scutellar lobe, postscutellax processes, prephragma, and postphragma; also the pleural clavicula, clavicle, coracoidal, tergal, prescutal, scutellar, mid postscutellar processes, and connecting ligaments.
MESOTHORACIC AND METATHORACIC WI-NGS. While there is a wide difference in the appearance and structural details of the e1vtra and the hind wings of beetles, they are evidently homologous and differ only in their modification in structure and function.

general position to that of the primary veins in the latter, thus conforming to the prevailing system in fully developed wings of all
insects. The primary trachew are costal, subcostal, radial, medial, cubital, and anal. In the elytron these occupy the marginal and alternating interspaces between the longitudinal strim or rows of

20 21 22 L 22a, 226 2
DORSAL

20 21 22 2=',2 23
VENTRAL
FIG. 29.-Dendroctonus: Left tibie, dorsal and ventral aspects. -20, punctatus; ?1, wticans; :2b, terebrans; 23, valns. (Original.)
punctures, while in the hind wing they follow approximately the
primary veins.
METATHORACIC OR HIND WINGS.
The hind or metathoracic wings (figs. 1, 20, and 30) are a third longer than the elytra or mesothoracic wings, under which they are folded when at rest. In consequence the veins toward the middle of the wings are flexible and adapted to the requirements of folding and unfolding.

44 THE SCOLYTID BEETLES.

Basal area (fig. 30).-The basal area is that in which the basal plates and head of the veins occur. In this area there are four
-ixillAr plates, which are more; or less common to insect ings ingreneral. These appear to bevlongr to the% wingy rather than to thie bodyV structures, and are'( her'e designated as scapular, subseapullar, flexor, radial, andl meia~il pl1ates. They are discussed in greater detail under Wing articulation.
I eins.-The six primary veins represented in the hi-nd wing are cta, subeosta, radlius I and 2, 1nedia 1 and 2, cubitus 1 and and 11n1,l, which Last is rudimentary.

latingy heid. It is broadest -where it is jondby the costa, an-d is strongly narrowed to its junction with the radius.
Radiuis.-The radius is an important vein. in giving additional rigidity to the median, distal, and costal areas and in foring the foling

Media.-The media is distinctly coiniecte(i with a basal, irregular, flexible medial plate, which is joined to the flexor, radial, and subscapular plates by membrane and flexible chitin. Near the distal
limit of the basal area there is an evident fohl or cross veinl connecting the base of the media with the base of the (e'bitus, from which it
proceeds outward to the hinge, and from this point two branches ex- C c. 4 3 2 1 StP
11to 1 8 7, 4; 21 hderoSpaces tend to the anal margin. c -Trachecc
Cubitus.-The cubitus rises from the outer border of the basal area and apex of the flexor and has two branches. Branch 1 extends to the margin. Branch 2 is short and
more or less rudimentary.
Anal.-The anal vein is evidently represented by the broad, short spur arising from the base of the cubitus, and does not extend to the margin.
Wing attachment.-The wing is attached to the body by chitinous dorsal and ventral integument, the latter arising from the dorsal margin of the epimxerum, and the former from the lateral margins of the prescutum, scutum, and scutellum, as indicated in the pupa. The heads or roots of the veins are attached by a system of connecting chitinous tendons and ligaments to the pleural and tergal processes and disks.
Wing articulation.-The principal
articulation of the wing is between FIG. 34.-Dendroctonus aulens: D)iagram of elytron, showing stria~, interspaces, and trachea'. the wing head formed by the costa Strhe 1-10; interspaces 1-11. Trachema: C, cosand subcosta and the condyles of tal; Sc, subcostal; R, radial; 31, medial; Cu,
cubital; A, anal. (Original.) the clavicle and coracoid processes cubital; A, anal. (Origina.) together with the scapular plate. The scapular plate is also connected with the prescutal process by articulating membrane and ligaments.
Pleural clavicula ("clavicula thoracique," Chabrier, 1820).-The position and function of the articular processes of the episternum and epimerum (fig. 20, pc), as represented more or less distinctly in all insects, are in Dendroctonus so strikingly analogous with that of the clavicle and coracoid in winged vertebrates as to suggest to the writer the same names. The giving of these names conforms with the practice of adopting for insect anatomy such of the nomenclature of ver-

48 THE SCOLYTID BEETLES.

tebrate anatomy as is applicable to parts in insects having the same or similar functions. Subsequently the writer's attention was called to the fact that the same idea was suggested to Chabrier.
In Dendroctonus the clavicle and coracoid processes are prominent and clearly defined, the condyle of the former being definitely connected with that of the head of the subcostal vein, which articulates between the condyles of the clavicle process and scapular plate. Chabrier's name clavicula has been adopted for the combined clavicle and coracoid processes.
Tergal processes (fig. 20).-The processes of the tergal area, which have more or less important functions as articulatory accessories, mlay be designated as prescutal, scutellar, and postscutellar.
Prescutal process.-The prescutal process is represented by a triangular extension of the posterior angle of the prescutum, and is of primary importance as an accessory to the scapular plate.
Scittllar process.-The scutellar process is represented by the thickene(l lateral margin of the lateral impression and by the produced, acute, anterior angle. It is attached along its lateral margin to a pleural tendon connecting the pleural disk to the flexor and subscapula. This process is also accessory to the flexor.
Postscutellar process.-The postscutellar process is an extension or arm of the anterior angle of the postscutellum, and has its apex attached to the pleural disk and to the pleural hook.
Lateral emnargination.-W hat is termed the lateral emargination is the emargination in the side of the scutum between the posterior angle of the prescutum and the scutellar process. It is present in most of the insects and appears to facilitate the functions of the flexor muscle.
Lateral imnpression.-The lateral impression is an impression to accOmInodate the flexor plate when the wing is at rest.
Basal Ielcimenits. -The basal elements of the wing which function as 1articuator accessories ire here referred to as head of costal vein, scapular, subscalpular, radial, medial, and flexor plates (fig. 30).
Ilead qfcostal rein (i). Thel( head of the costal vein is produced beyond its fus( connection with the head of the subcosta. It is connected to the hea(l of the clavicle by a ligament, and evidently fu lic tions in exten(ling the wing forward as well as in contributing to oth 1er motions.
Scapular plate (a).-In form and( function the fundamental basal plate, which we here (call scapular plate, is very suggestive o()f the scapula of vertebrates, but its peculiar functions require quite differnilt tergal (conmnections. It is joined by ligaments to the prescutal pr)(oess and lateral largiln (of the 1presclutal lobe in stuchl a manner as t facilitate part of its functions that o)f unfolding, elevating, and hlepressingr thle \Vllig. Its colle articulates directly with the

T'lE GENUS DEND1CT()NS. 49

dorsal or inner edge of the head of the sub),sta and within the cla vicle condyle.
Subscapular plate (b).-The subscapular plate is more (compilicat ed in its structure than the scapular plate, to which it is a direct accessory, the two being closely joine(l by articulating ligament. It flInclions as an intermediate patella-like connect ion of t he syst em of tendons which connect the pleural disk at the head of the plural niumscle with the flexor, head of scapular plate, head of coracoidal l)r(cess, head of subcosta, etc. Therefore it must be of fundamental importance in wing motion.
Radial plate (d).-The radial plate is represente(l b)v athin chitinous piece connecting the radius with the sub)scapula.
Medial plate (e).-The medial plate is of flexible ciitin connect ing the media with the flexor and subscapula.
Both the radial plate and flexor plate evident lY funct ion as articnlating accessories.
Flexor plate (c).-The flexor plate comes next to the scapular plate in its fundamental importance in wing connection and( articulation, and is especially fitted in structure and( muscular connection for its primary function of flexing and longitudinally folding the wing, as well as in the reverse action of contributing to its outward extension and rigidity during flight.

MESOTHORACIC WX1NCS Ot ELYTRA.
The form and general structure of the elytra are shown in figures I and 31. They are oblong, rigid shields, with a subacute apex and a truncate declivous base and a produced articulating head. The structure, like that of the metathoracic wing, consists of two layers of integument inclosing the tracheal and circulatory system, but instead of the dorsal and ventral layers being partially composed of flexible membrane, they are chitinous throughout. The ventral layer is thin and smooth, while the dorsal one is thick and deeply sculptured.
Tracheation.-The six primary trachea (figs. 31, 34) occupy the marginal and the alternating longitudinal spaces between the rows of punctures. Each has numerous fine lateral branches passing between the punctures into the intervening interspaces, producing a network of fine tracheae, with the punctures representing the mesh. Thus we have a probable explanation of the primary cause of the system of punctures in the elytra and the longitudinal and tranverse thickened spaces between them. The thickened and elevated areas are due to a concentration of chitin over the tracheal and circulatory canals, while the punctures and grooves are the points of adhesion or junction of the two layers to form the walls between the canals.

50 THE SCOLYTID BEETLES.

Sculpture.-The dorsal chitinous layer presents many and varied characters of sculpture, the principal elements of which are the stria, including the longitudinal impression and rows of punctures. The interspaces are longitudinal spaces between the striv~. The rugosities of the interspaces and stria and the elevated rugose basal margin are all characteristic elements of sculpture. There are ten strike and eleven interspaces. For convenience in referring to the variable characters, these are numbered, beginning with those next to the dorsal suture, when the elytra are closed, or with the posterior or anal margin when the elytra are open. Thus we have interspaces 1 to 11, and strim 1 to 10 (figs. 31, 33).
Interspaces.-In an ideal system (fig. 34) interspaces 1 to 5 are continuous toward the apex with 11 to 7, leaving 6 independent between 5 and 7. The primary trachee occupy interspaces 1, 3, 5, 7, 9, and 11. There is, however, more or less variation and modification in the elytra of beetles from this ideal arrangement and especially upon the distal ends and their junctions with each other on the declivital area. In Dendroctonus interspace 1 is usually more elevated and continuous to apex, where it joins the very narrow marginal 11; 2 is less elevated to flat, narrowed toward apex, and joins the very narrow and obscure submarginal 10, which becomes broader and distinct toward the base; 3 joins the distinct 9; 4 joins
6 around the apex of 5, and also joins 8 around the apex of 7.
Strix.-In the ideal arrangement (figs. 1, 31, 34), strim 1 to 5 are continuous with strim 10 to 6, but the usual arrangement on the declivity in this genus is 1 to 3 continuous with 10 to 8, while 4 is continuous with 5, and 6 with 7. The strial punctures range from small to coarse and from very distinct to obscure, and are sometimes variable inii size and appearance in the same species. The prevailing condition, however, of relative obscurity or distinctness in different species is of considerable specific importance. The strial imi)ressions also vary within the genus from scarcely to distinctly or deeply impressed, and the prevailing condition within the species is of considerable value. The elytral declivity, as is usual in the scolytidl beetles, bears some of the more important specific and secondary sexual characters.
The other character-bearing areas of the elytra are the lateral, nwedian, and the d(orsal toward the vertex and base.
Vestiture. -The elytra are more or less distinctly clothed with short or long hairs. The length, size, arrangement, aid areas occupied furnish important taxonomic characters in distinguishing the major and some of the minor divisions, as showVn in the synoptic table. A p)rogressive modification in vestiture is from very short hairs over the entire surface to longer hairs and sparsely arranged

THE GENUS DENDROCTONUS. 51

bristles toward the vertex of the declivity and on the declivity itself, or to fine and coarse long hairs over the entire surface.
Lateral fold or postal groove (fig. 31, n, o).-In the costal edge of the elytron, from near the base to the median section, there is a lateral or costal groove for the reception, when the elytra is closed, of the corresponding produced and acute dorsal edge of the episternum. There is also a deeper and broader groove in the median section of the costal area, for the reception of the produced dorsal edges of hypopleurites 3 and 4. According to LeConte and other writers, this lateral groove is an important subordinal character.
Sutural tongue and groove (fig. 33, a-j).-In the sutural edge of the left elytron there is a deep lateral groove and produced ventral edge for the reception of the corresponding produced lateral edge or tongue of the right elytron, thus forming a tongue and groove suture. Toward the apex both the ventral edge of the left and the tongue of the right are dilated to facilitate the locking of the elytra when they are closed.
Stridulating accessores.-In the male there is a transversely and microscopically sulcated area on the ventral surface toward the suture and apex of each elytron (fig. 33). When the elytra are closed this forms a continuous filelike surface situated directly above the stridulating scraper of the seventh abdominal tergite or propygidium. A peculiar, independent, upward and backward motion of the propygidium brings the scraper in contact with the file, and thus produces a peculiar chirping sound which is quite audible to the human ear.
The exact location of the organs of hearing in these beetles has not been determined.
Basal and pleural elements.-The basal process, or articulatory arm (fig. 32) of the elytron appears to represent the fused heads of the costa, subcosta, and radial veins. The usual scapular, subscapular, flexor, and medial plates are quite definitely represented, and occupy the same relative positions as in the metathoracic wing. The pleural clavicula are represented in the mesothorax by the clavicle and coracoidal processes, which are fused beneath the anterior dorsal angle of the episternum to form the condyles (fig. 19). The clavicle disk is not represented, unless it is by a narrow free piece attached to the costal angle of the elytral process, and represents the parapterum or extensor plate, to which the extensor muscle is attached.
INTERNAL ANATOMY.
While some study has been made of the internal anatomy of these beetles it has not been sufficient to warrant a detailed discussion in this connection.
134440-11- 5

52 THE SCOLYTID BEETLES.
DIGESTIVE SYSTEM.

The general character of the digestive system is shown in figure 35, and no further explanation is necessary in this connection than that given in the legend under figures 35 and 36. In figure 36 some of the details of the internal anatomy of the fore intestine are shown, and especially the structures and S elements of the proventriculus and
aboophauo, hypopharynx.

SSECONDARY SEXUAL CHARACSCrop
A TERS.
'Proentriculus While there are certain clearly defined secondary sexual characters
: in these beetles, they have not been
-- recognized by other writers, and
"4 i ventriculus they were not found by the present writer until after much detailed I study of the genus. When they
.. were determined it was surprising
B how such prominent characters
b could have been overlooked. Thus
-'
we have another example of how thoroughly familiar one must be with a given group in order to recd._ ognize and properly interpret the
B significance of characters in strucrap o e -surs-ture, sculpture, vestiture, etc. In
1.1talpiglhlar tubules' fA
fi the first subdivision of the genus
I ',cotrn the females are distinguished by a
Sc transverse ridge across the anterior
area of the pronotum, while the ,,, males are distinguished by the ab0 sence of this ridge and by more
prominent frontal tubercles which FIG. 3 .-Dendroetonus valens: I)igestlve organs are separated by a deeper frontal of adult. A Fore intestine; B, mid intestine; C, hind intestine; a, anterior section of mid in- groove. testine; b, median section of mid intestine; c, In the second subdivision the posterior section of mid intestine; d, cecal glands; e, ilcum or small intestine; ,J. base of 4 females are distinguished by the malpighlan tubes; base of 2 nsalpighian tubes. smoother and more shining elytral (Original.) declivity. In the third subdivision
the females have the elytral declivity distinctly more rugose, while that of the males is smooth and shining. Thus we have a reversal of the secondary sexual characters within the same genus, which is an unusual occurrence.

THE GENUS DENDROCTONUS. 53

In the fourth subdivision the sexes are more difficult to recognize, but the males are distinguished by stouter, more opaque mandibles, broader front, and by a narrower and more elongate antennal club. Whenever there is doubt as to the sex of an individual it can be settled by examining the pygal segments for the characters shown in figures 23 and 24.

The general structure, proportions, and anatomical details of the Dendroctonus pupa are shown in figures 37 and 38.
Among the distinctive generic characters are the large prominent head and broad pronotuin, while among the divisional and specific characters are the sculpture, armatures, etc., of the head, pronotum, elytra, and abdominal segments, as shown in the figures and defined in the synoptic tables and descriptions.

54 THE SCOLYTID BEETLES.

IHead.-The elements of the adult head recognizable in the young pupa are the antenna, mandibles, maxillw, labium, and what appears to be a well-developed labrum, which extends to the middle of the mandibles. Evidently, however, this does not represent the labrum or even the clypeus, but is a pad to accommodate the development of

22

"S EI; -4 I

f- l
4P

t 0
Aki

," .." ...-.

N- -- """P --;

XYOH, /:IO G H Y

the long epistomal bristles. The frontal spines in examples representmng different divisions and species are variable in size and position and are of considerable taxonomic importance. The antenna do not extenI to the base of the pronotum or scarcely beyond the mouth parts, and the club (loes not extend beyond the lateral margins of the
fOLU.ID.
6 :'a gs ;

Prothorax .-The form of the pronotum corresponds to that of the adult and its relative proportions are of some value in dlistinguishing the species. The number an(1 position of the frontal spines are fairly constant in a species, although they vary in prominence with

of the spines. The median process of the scutellumn is prominent and the posterior or scutellar ridge is distinct. The base of the elytra is oblique and elevated, and( its integument continuous with that of the tergum and scutellar ridge. The sternum is situated between the mesocoxate and the trochantins of the prothoracic leg.
Mtathora.r.-The metatergum is prominent and has the usual dorsal or scutellar groove. The transverse posterior or scutellar ridge is distinct and joined at its ends with the basal angle of the wing pads. Each of the scutal lobes bears a pair of spines. It differs from the metatergum of the adult mainly in the absence of the prescutum and postscutellum, as defined by external elements.
Abdol uinl tergites (fig. 38).-There are nine tergites visible dorsally and a very small tenth visible ventrally. Tergites 3 to 6 are armedI more or less distinctly with dorsal, lateral, and pleural spines. The dorsal spines are located each side of a narrow dorsal groove; the pleural spines on the epipleura posterior to the spiracles, and the lateral spines are situated between the dorsal and pleural. The size of the pleural spines and the size and number of the dorsal and lateral ones are quite variable and of considerable importance in defining the minor divisions. Tergites 7 and 8 are usually unarmed, b)ut, as in tlhe adults, show sexual differences in their relative prominence; 9 has the median lobe short, but the pleurites are greatly enlarged and( each is armed with a prominent caudal spine.
Thie four transverse divisions of the segments are quite clearly indicated in tergites 1 to 6. 'ergites 7 and 8 show two divisions, the first representing prescutal and the second the scutal and scutellar coImbined, while terIgites 9 and 10 are undivided. It is interesting to note that the d(orsal and pleural armatures are borne by what is evidently the scutellar division, and that the spiracles are in the prescutal division, thus indicating that the prescutal represents the first p)rimary division anl the combined scutal, scutellar, and postscutellar reI)IeseIlt t lie second primary division.
A bdoul;ialsternites.-There are eight exposed( abdominal sternites. Theev are sternites 3 to 10, 1 and 2 being concealed beneath the mnetacox~, as shown in figure 38.
Abdotill ple ur-tes.--Epi)leurites and hypopleurites 1 to 8 are clearly (lefine in the removed abdomen (fig. 38), but in 9 and 10 only the epipleurites are represente(l, as ind(licated(l by the pleural suiture. Tlwe )leural suture I is distincMt to the ninthi segment, where it joins the lines marking the dorsal and ventral limits of the pIleural division.
SJira(Tces.. 'Tlhere are nine sp)iracles in each sidle of the body, one large ,esot loacic spiracle situatedl between the posterior lateral Imargil of t1w p)rotl()orax anl the anterior ventral angle of the elytral pad, and eight abdominal ones, each in its respective epipleurite.

THE GENUS DENDROCTONUS. 57

The metathoracic spiracle is not represented. Spiracles 3 to 8 are exposed when the elytral pad is in normal position, but spiracles 7 and 8 are very small and obscure. Thus the pupa has the same number of spiracles as the larva, while in the adult there is an addl(litional one, although that of the eighth abdominal tergite is apparent ly rudimentary. The larva lhas one thor acic spiracle, apparently in the prothoracic segment. The pupa has one in the mesothoracic, and the adult has one in the mesothorax and one in the metathorax.
Legs.-The front and middle legs are exposed, while the hind legs are partially concealed beneath the elytra an(1 wing pads. The front coxw are large and contiguous, the anterior fourth covered by the maxille and labium, and the posterior margin extends over the anterior margin of the mesosternum. The middle coxw are partially hidden by the apex of the front tibia and its tarsus. The hind coxe are for the most part exposed, and distinctly separated by an intercoxal area. The positions of the different parts of the legs in their relation to the exposed structures are shown in figure 37, and are of considerable taxonomic importance. The apical and subapical spines of the femora are also of considerable importance as distinctive characters.
LARVA.
The structure and general characters of the larva are shown in figure 39. It is of the subcylindrical, wrinkled, legless type common to all of the true Rhynchophora, and also has the form of mouth parts characteristic of the larve of this suborder. There are three thoracic and ten abdominal segments, the tenth being represented by the anal lobes. The four longitudinal divisions, viz, one sternal two pleural, and one tergal, are clearly represented in all of the segments. The tergal division occupies nearly one-half of the circumference, the two pleural divisions together about one-fourth, and the sternal division slightly more than one-fourth. The head is much narrower than the first thoracic segment and but slightly longer. The three thoracic segments together, or the thorax, is about one-third as long as the abdomen. With the exceptions of the scattering hairs on the head and on the scutellar lobes of the thoracic and abdominal segments, the body is without distinguishing vestiture.
EXTERNAL CHARACTERS.
Head (figs. 40, 41).-The head is by far the most important part of the body as a bearer of taxonomic characters in the larva. The general structure is shown in figure 40, and the anatomical details in figures 41 and 42. All of the primary elements of the adult head are represented, but they are much more simple in their structural details. The more striking differences in the larval head are found in the

58 THE SCOLYTID BEETLES.

presence of clearly defined front, clypeu-s, and labrum, in the articulation of the mnandibles, and in their rudimnentaryv hypostoxna.
Labruin (figs. 40, 41).-The labrium is prominent, the dorsal area twice as broad as long, about one-third narrower than the clypeus, but nearly as long, with the apical margin broadly rounded, truncate

IQ I

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--

C1 I

C'

Or faintly emlarg(inlate, aiid with -several apical papilla,. The median (lorsil "Irva bears, several long hairs anii W)sihl lvt(l dark spots where t he epiphlaryngreal bracons are at tachied. The latter somewh'lat. resoeible the miandibular hooks of dipterous larv.T, and mayr or may not repr-esent paired eleitos o)f the hieadl of a primitive arthropod.

THE GENUS DENDROCTONUS. 59

Whatever their origin may have been, the present function is to support the epipharynx and also serve as chitinous attacluhments for the depressor muscles of thelabrum. They are covered( by the epipharynx
and extend down and back to the esophagus and to a point beneath the base of the clypeal area.

Epistoma.-The epistoma is quite clearly defined as a thickened transverse area between the clypeus and the frontal area. It does not extend laterally to the frontal sutures, but the ends, where they join the pleural ridge or pleurostoma, bear the condyles for the dorsal articulation of the mandibles. As in the adults, this area is quite vari0

o o

-o
.,., .. .,,,. .r 0

able within the genus. It is elevated to flat, with the anterior marin ranging from curved to nearly straight and the lateral angles elevated or slight ly produced so as to form the rigid support for the dorsal
N2
'0' 'W. I

condyoles.

l iypostoma.-The hypostoma is not rephesented by rn exposed piece, but by the apodeme which forms the thickened lateral and sub939

THE GENUS DENDROCTON US. 61

lateral margins of the maxillary foramen. The anterior end supports the fossa (g) of the ventral articulation for the mandible, and the ventral end supports the condyle for the articulation of the maxillary cardo. It is connected across the gular space by the entogular plate.
Pleurostoma (fig. 40, e).--The pleurostoina is represented by the thickened lateral margin of the oral forainmen. The dorsal end contributes to the rigid support of the dorsal articulation for the mandible and the ventral end to that of the ventral articulation.
Front.-The front is situated posterior to the epistomna and between two oblique sutures which converge from the anterior angles to the epicranial suture. The median area is quite variable within the genus. It may be flat and smooth to elevated. In the latter case it may be small, smooth, and convex, or prominent, transverse, and rugose.
Epicranium.-The epicranium is represented by the dorsal areas
of the two large lobes each side of the distinct epicranial suture and frontal area. These lobes are continuous throughout the occipital and genal areas and accommodate the very large retractor muscles of the mandible. The genal areas are connected by the broad entogular plate.
Occipital foramen.-The occipital foramen is situated in the posterior ventral section of the head and occupies about one-half of the ventral area. It is bounded posteriorly and laterally by a broad entoccipital rim and anteriorly by a subchitinous rim. The occipital apodeme arises from the posterior margin, and extends anteriorly immediately beneath the epicranial suture.
Entogular plate (fig. 40, i).-The entogular plate is the subchitinous plate which forms the entocranial connection between the genal areas and anteriorly between the lateral sections of the hypostoma. It is covered by the submental lobe, part of the muscles of which are attached to the posterior angles and posterior margin.
Maxilla (fig. 41).-The maxille are quite simple in structural details. The cardo is present and distinct. Its basal articulation and attachment are by ligaments and a fossa to a condyle supported by the hypostomal apodeme. Its anterior attachment to the stipes is by articulating membrane. The median section is not divided into stipes, subgalea, and palpifer, but is one continuous piece with the anterior inner angle produced into a lacinial lobe which is armed with a number of papille situated on a membranous integument. The palpus is 2-jointed and telescopic as usual. The relative proportions, sculpture, and vestiture are shown in the figure.
Labium.-The labium of the larva is very different in structure from that of the adult. The submentum is represented by a lobe which is very broad and differs but slightly from the sternal lobe of the prothoracic segment with which its posterior integument is directly connected. The lateral integument is continuous with that

62 THE SCOLYTID BEETLES.

of the maxilla and the anterior angles are extended forward to the base of the palpi. The mentum is represented by the median triangular chitinous plate, the posterior section of which is produced and narrowed, and the anterior median section is produced anteriorly between the palpi and supports the ligula. The short, conical, 2-jointed palpi are situated on the anterior angles of the mentum and are scarcely longer than the simple lobelike ligula which bears a few simple papilla.
lypopharynx and epipharynx.-The position and character of these important elements of the oral opening are shown in figures 40, D, and 41, B.
Mandibles (fig. 42).-The mandibles are stout, with the laterodorsal surface rugose, except toward the apex, which is produced into an apical tooth; the inner edge toward the apex is provided with a subapical tooth and two small irregular medial teeth. The condyle of the ventral angle is globular and fits into the concave fossa (fig. 40, g) of the hypostoma, while in the dorsal articulation the fossa is borne by the mandible and the condyle by the epistoma (fig. 40, d). The small extensor muscle is attached to the outer basal margin midway between the condyles, while the large and powerful retractor muscle is attached to the margin of the more produced inner angle, thus riving a direct lateral motion to the mandibles.
Tergites (fig. 39).-The dorsal area of the tergum of the prothoracic segment is undivided, but evidently represents the scutum (e) and scutellum (f). The dorsal area of the mesothoracic and metathoracic segments has two divisions. The anterior division evidently represents the prescutal lobe (g). There is evidence of a scutal lobe (e) on the lateral area of both segments, as indicated in the abdominal tergites, where the scutal lobe appears between the anterior and the posterior lobe. Thus the latter evidently represents the scutellar division, or scutellar lobe (f).
Sternites.-The sternum of each of the segments has three sections, interior, median, and posterior, or sternal (h), sternellar (i), and poststernellar (j). In the thoracic segments the sternal is the larger and projects posteriorly over the middle of the sternellar lobe, which is represented by a coxal lobe each side of the sternal section. In some of the species these lobes have a median chitinous spot or foot callus at the point where a foot occurs in the legged larve of other Coleoptera. The abdl)(lominal sternites have the same number of sections, but the sternellar section i! not covered by the sternal.
Pleurites.-The pleurun of each segment is divided longitudinally by an irregular pleural groove or suture (w). The lobe immediately below the groove at the end of the sternites may be referred to as the hypopleural (k) and that immediately above it as the epipleural (1). The hypopleura of the thoracic segments represent the episternum,

THE GENUS D)ENIROCTONI'S. 63

and the epimerum is obscurely repl)resented by the epipleiurn'l, hot h of which are but little, if at all, different from those o()f t ie ab(lomnen. The epipleural lobe of the prothoracic segment has a sp)iraele, while those of the mesothoracic and metathoracic segments are without a spiracle, but has lateral lobes or areas for the einbryonic wing.
Spiracles.-It will be noted in figure 39 and Plate VII f that the prothoracic segment has a spiracle situated on the epipleurite near

Ja

aa

0 D
69

I(
C
bb

B 9

k d

A

FIG. 42.-Dertdroctonus valens.s: Mandibles of larva. A, Latero-dorsal aspect; B, dorsal aspect; C, lateral aspect; D, apical aspect; a, apical tooth; b, subapical tooth; c, median tooth; d, molar tooth; e, extensor tendon: f, retractor muscle disk; g, retractor muscle; h, extensor muscle; i, dorsal fossa; j, dorsal condyle; k, ventral condyle; 1, basal ridge. (Original.)
the epipleurite of the mesothoracic segment. The writer is not certain as to whether or not this really belongs to the prothoracic segment or, as in the abdomen, to the anterior or prescutal division of the mesothoracic segment. The metathoracie segment is plainly without spiracles, but the abdominal segments 1 to 8, inclusive, have spiracles which are more or less distinct, being rather obscure in the first division and in section a3 (see P1. I) and without lateral tubercles, while in section a4 and subdivision D both the spiracles and

64 THE SCOLYTID BEETLES.

spiracular tubercles (Plate VIII) are distinct. The ninth segment is without spiracles.
C7 itinous plates.-In some species (division I) there are no distinct chitinous plates or tubercles, while in others, section a4 and subdivision D, they are present and, excepting Dendroctonus micans, become more distinct toward and including subdivision D, in which the dorsal plates of the eighth and ninth abdominal segments are distinctly armed.
DIGESTIVE SYSTEM.
The peculiar characters of the digestive system of the larva are illustrated in figure 43, showing, at right, a median longitudinal section through the body from the oral to the anal opening. In every respect the anatomical details of the digestive system are much more simple in the larva than in the adult. The same primary divisions of fore, middle, and hind intestine are represented and there is the same number of malpighian tubes, but the fore intestine is very simple as compared with that of the adult, the crop and proventriculus being scarcely different in general details from the esophagus.

EGGS.
The eggs of Deudroctonus have not been studied in detail, but they are short, oval to oblong-oval, pearly white and shining, and apparently without distinctive generic or specific characters.

PHYSIOLOGICAL CHARACTERISTICS.
In addition to the morphological characters which serve to distinguish the genus, there are certain physiological characteristics peculiar to the species of the genus which serve as additional evidence of distinction. Indeed, it becomes more and more evident that a correct interpretation of natural groups of individuals, termed species, an(1 natural groups of species, termed genera, must be based not alone on a common plan of structure or similarity in one or more anatomical elements, but that, in order to come nearer the truth, the morphologic evidence of specific distinction must be supplemented by physiologic and b)ionomic evidence. Some of the physiological features common to the species of this genus, and more or less peculiar to them, are found in the character of their brood galleries, in their habit of attacking living trees, in their concentration of effort to overcome the resistance exerted by the tree attacked, and especially by their ability to manipulate and to dispose of the quantities of resin which flow into their burrows in the living hast and cambium; lastly, in their intimatte b)ionomic relations to definite genera and species of conifers.a
a See, also, physiological characteristics of the species, as given in the forthcoming Bulletin No. 83, Part I, which deals with the bionomic and economic features, and other characteristics peculiar to the major and minor divisions as defined in the synopt ic tables of gUileries4, host trees, and distribution in the present paper (pp. 76-79).

SPECIFIC DISTINCTIONS.
In the literature on Scolytidw, and, for that matter, on almost any group of insects of special systematic and economic importance, there is much confusion, due to different interpretations of specific distinction. Some authors have combined many described species into one, while others have recognized many distinct forms among those heretofore included in one species, and have proposed as many different names for them. It is evident that whenever "lumping" or "splitting" is necessary for the clear definition and recognition of a species it should be (lone, but it is equally evident that neither should be attempted without an adequate knowledge of at least the genus represented, in order that the true characters of specific distinction may be recognized from those which serve to distinguish the genus or the major and minor divisions of higher rank than the species.

RANGE OR LIMITS OF SPECIFIC VARIATION.
The determination of the range or limits of variation in characters utilized for the distinction of a species is one of the most troublesome questions with which the systematist has to deal. With one or a few specimens the line separating one recognized species from another may be distinct and definite, but as the number of specimens from different localities increases the line of distinction from allied forms often becomes less and less distinct until it is almost or quite obscure. Here is where expert judgment, based on experience and a technical knowledge of the special group involved, is required in order to decide whether or not two heretofore recognized and closely allied species should be kept separate or be combined. The recognition of prevailing variants or constants, or of forms having abnormal or normal morphologic and physiologic characters, is of special importance in this connection, as is also the recognition of the disturbing factor of parallel modification in characters and habits among species of the same genus, as well as among those of different genera.
If the variants connecting two allied groups comprise only a small percentage of the individuals, they may be considered as departures from the constants of the species more nearly represented, and thus the groups so slightly connected will serve the purposes and requirements of species and neither of them should, in the writer's opinion, be designated as a named subspecies, race, or variety; but if, on the other hanl, the connecting variants comprise a large percentage of in(i vidtuals, anl no other characters sufficiently distinct and constant can be found by which indivi(uals may be readily referred to one or the other of the heretofore recognized species, it would indicate that the two are not specifically distinct.

THE GENUS DENDiIOCT0ONUS. 67

PROGRESSIVE MODIFICATIONS.
The writer has been forcibly impressed with the prevailing principie of progressive modification in relative proportions in form and structural details in scolytid and other beetles. Whenever these modifications in relative proportions are available for the statistical method of analysis it is often possible to express in numbers the difference between species and to indicate clearly the lines of modification and rates of departure among the species of a genus or larger group.
There are some good examples of this principle of progressive modification in the genus Dendroctonus, which is manifested not alone in the adults, but in the pupae, larvae, and character of work, and it is most interesting and significant to note that the modifications are in the same general direction in all cases. When the species are arranged in the order indicated by these modifications and other characters, the species of the first division to the last of those of the second division are found to be modified from small to larger size, the extremes being represented by D. frontalis, with the minimum length of 2.5 mm., to D. valens, with the maximum length of 9 mm. Naturally we find the same rate of difference in size of the immature stages and galleries. This same tendency toward increased size is manifested within each subdivision, section, or minor group of allied forms and appears to be a prevailing principle throughout the Scolytidw, and thus serves, in connection with other lines of modificatoas one of the first guides to a natural arrangement or classification of the species. In Dendroctonus the progressive modification of characters other than size is shown or indicated as follows:
PROGRESSIVE MODIFICATION OF CHARACTERS IN THE GENUS DENDROCTONUS, ADULTS.
Primary characters.
Body slender to stouter.
Head large to smaller.
Prothorax long to shorter.
Pronotum with sides nearly parallel to distinctly narrowed or constricted anteriorly.
Pronotum, as broad as elytra to narrower.
(A mean composite ratio of the above gives a number which expresses the relative proportions and serves as a species index.)
Front grooved and tuberculate to convex and smooth.
Elytra without long hairs to long hairs over entire surface.
Tibia from slender to broader with a tendency to dilate toward the apex. Funiculus of antenna with second joint long to shorter.
Secondary sexual characters.
Front of head with sexual differences to similar or alike in both sexes.
Pronotum, with sexual differences to alike in both sexes.
Elytral declivity without sexual differences to distinct differences.
Declivity rugosities small to coarse, smooth in female to coarse in male or reversed.
Mandibles alike or similar in both sexes, to much stouter in the male.
134440-1 1-6

68 THE SCOLYTID BEETLES.
PUPB.
Front of head grooved to convex.
Body spines small to coarse.
LARVE.
Body simple, without chitinous plates or hairs, to distinct chitinous plates and more prominent hairs.
Eighth and ninth abdominal segments without chitinous plates to with plates, these last unarmed to armed.
Spiracles simple to complex, smooth to tuberculate. Epipleurites without tubercle, to prominent tubercle.
GALLERIES.
Long and winding to short and straight.
Eggs isolated to grouped and massed.
Larval mines hidden to exposed and short to long.
HOSTS.
From one genus to many genera, and from one species to many species. D. brericonis is found in pine only, while D. ralens infests Pinus, Picea, and Larix; D. snimplex infests Larix only, and D. pseudotsugx infests Pseudotsuga and Larix.

DISTINCTION OF MAJOR AND MINOR DIVISIONS OF THE GENUS.

In a comparative study of the species of the genus to determine their relative positions, as indicated by degrees of resemblance or difference, they are found to fall according to progressive modification of characters into major and minor divisions, which may be designated as divisions, subdivisions, sections, subsections, series, and subseries, to the smallest practicable minor division of the genus, viz, the species.
In this classification of the genus the rank of a primary division may be that of the subgenus of some authors and the lower series of closely allied species may be recognized by some systematists as occupying the rank of subspecies, races, or varieties; but the writer has been gui(led by the belief that the principle of a less restricted range of generic and more restricted range of specific distinction will contribute toward a more correct knowledge of the forms of life than if the reverse principle is followed.
The classification of the species of a genus into major and minor divisions is necessarily arbitrary, and is subject to changes as may be suggeste(l by increased knowledge and(l the addition of species. T() a more limited(I extent, the d(lesignation of a species is arbitrary an(l with ad(lditio()nal material and information is subject to revision; but since the species, next to tihe individual, is the constant or unit of classilicnation and investigation, it should represent the lowest practical diisioi of(1 a genus that is recognizable from a description of a ty)ida f~(rI or by comparison with the type on which the description was )as(.

THE GENUS DENDROCTONUS. 69

PLAN OF SYNOPTIC TREATMENT.
The plan here applied for the classification and synoptic treatment of the species of the genus is one which appears to be most available and practicable for the clear definition of the progressive mo(lification of taxonomic characters and for indicating the relative systematmc positions and limits of the major and minor divisions an( the species. It is not radically different from some of the mor, genenlly adopted dichotomous systems, and it conforms to the primary ())jects of a, synopsis in that it provides (a) for a direct comparison of opposing characters, (b) for a direct line of references leading down to the specific characters, or vice versa.
With this method of indicating the supposed natural relation of the species, the described characters of the major and minor divisions and sections, together with those of specific distinction, serve as a description of the species. Thus, division I, subdivision A, section a2, subsection b2, series c2, defines the characters common to species 6, 7, and 8, which are separated by their respective specific characters. Some additional advantages of this method are the consecutive arrangement of letters and figures which throughout a given table are not duplicated. The Roman numerals indicate at once the primary divisions, the capital letters the subdivisions, and the combined small letter and Arabic numeral the sections, subsections, series, etc., to any desired limit. The reference from right margin to center, instead of to left margin, is also an advantage in defining
the limits of a major and minor division. It also provides for full paragraphs, thus economizing space and cost of printing.
SYNOPSES OF MORPHOLOGICAL AND PHYSIOLOGICAL CHARACTERS.
SYNOPSIS OF ADULT CHARACTERS.
Pronotum somewhat elongate and as broad as elytra; not distinctly narrowed anteriorly except in subdivision B; anterior dorsal half of elytra without long hairs.
Division I, pages 69.81.
Pronotum stout; usually narrower than elytra, and distinctly narrowed and constricted
anteriorly; anterior dorsal half of elytra normally with long hairs, except in terebrans ............................................... Division 11, pages 71, 116.
DIVISION I.
Body somewhat slender, pronotum but slightly narrowed anteriorly; elytral declivity
with second stria straight, second interspace not distinctly broader or narrowed
toward apex; head with frontal groove and tubercles except in con trexfrons.
Subdivision A, pages 69, 81.
Body stout; pronotum distinctly narrowed and constricted anteriorly; elytral declivity with second stria curved, second interspace broad and distinctly narrowed
toward apex; head without frontal tubercles or groove.
Subdivision B, pages 71, 105.
SUM UDIvIsio-; A.
Elytral declivity without long hairs .......................... Section al, page 70.
Elytral declivity uwth long hairs ...--------------.--------------- Section a2, page 70.

SUBDIVISION D.
Females: Head with front moderately broad; mandibles shining, moderately stout;
antennal club broader ...................................... Species 22 and 23.
Males: Head with front broad; mandibles opaque, stout; antennal club narrow, more
elongate and less compressed ............................... Species 22 and 23.

SYNOPSIS OF PUPAL CHARACTERS.
Vertex of head distinctly to faintly grooved, and with two small or prominent frontal
spines on or toward the vertex each side of groove ................... Division I.
Vertex of head faintly impressed, flat or convex, and with two small, widely separated
frontal granules toward vertex .................................... Division II.
DIVISION I.
Frontal spines small; elytral pads smooth; abdominal tergites 2 to 6 with or without
small pleural spines .......................................... Subdivision A.
Frontal spines large, prominent; elytral pads rugose; abdominal tergites 2 to 6 with
prominent pleural spines ..................................... Subdivision B.

74 THE SCOLYTID BEETLES.

SUBDIVISION A.

Anterior and middle femora smooth; abdominal tergites 3 to 6 with small pleural spines,
1 and 2 without distinct dorsal and lateral spines. Section al, Species 1, 2, and 3. Anterior and middle femora with small apical spines ................... Section a2.
Section a2.
Abdominal tergites 2 to 6 without distinct pleural spines; 7 and 8 with small granules............................................................. Species 4.
Abdominal tergites 2 to 6 with small pleural spines of equal size; 7 and 8 with small
granules......................................................... Species 5.
Abdominal tergites 1 to 6 with small pleural spines, increasing in size; 7 and 8 smooth.
Species 8.
SUBDIVISION B.
Apex of anterior and middle femora with two spines.................. Species 9.
Apex of anterior and middle femora with one spine; abdominal spines and elytral
rugosities coarser than in species 9................................ Species 10.
Apex of anterior and middle femora with two spines; abdominal spines apparently less
prominent than in species 9 and 10............................... Species 11.
DIVISION II.

Vertex of head fattened or faintly impressed; apex of front and middle femora smooth
or with minute granule; abdominal tergites with pleural and dorsal spines moderately prominent............................................... Subdivision C.
Vertex of head convex; front and middle femora each with a minute pilated, subapical
granule; abdominal tergites with less distinct pleural and dorsal spines.
Subdivision D.
SUBDIVISION C.

Vertex of head moderately impressed: anterior and middle femora without apical spines;
abdominal tergites 2 to 6 with very small pleural spines; 4 to 6 with small dorsal spines, all w ith pale tips.......................................... Species 14.
Vertex of head distinctwly impressed; abdominal tergites 2 to 6 with distinct pleural
spines, and 3 to 6 with distinct dorsal ones ......................... Species 15.
Abdominal tergites 2 to 6 with very small pleural, lateral, and dorsal spines, all with
dark tips....... ................................................. Species 17.
SUiDIWSION 1).

Abdominal tergites I to 6 with moderately small pleural spines, 2 to 6 with small dorsal
and lateral ones, all with pale tips ................................. Species 22.
Same as preceding, except spines have darker to black tips ............. Species 23.

SUBDIVISION B.
Front of head with posterior apex subacute; frontal elevation moderately stout in the
middle; clypeus with faint median tubercle toward the base......... Species 9. Front of head with posterior apex subobtuse; frontal elevation stout slightly poster(ior
to the middle; clypeus with a faint median groove and elevation toward base.
Species 10.
Front of head with posterior apex subacute; frontal elevation narrow, situated in the
middle, not more distinctly elevated toward suture; clypeus with faint median groove, without elevation.......................................... Species 11.

Larval mines separated beyond the middle ------------------ Species 14, 15, and 16.
Subsection W.
Larval mines usually not separated beyond the middle, but forming a common chamber.
Species 19 to 21.
SUBDIVISION D.

Egg galleries broad to very broad, short to very long, straight to winding; larval mincs
forming a large common chamber ............................ Species 22 and 2:1.

TABLE OF DISTRIEBUTION.a
America, north of Guatemala, and in northern Europe ........... ....... The geDuz.

DIVISION 1.
SUBDIVISION A.

North American continent, in South Atlantic and Gulf States and Southwestern
States, southward to Guatemala and northward in Sierra Nevada and Cascade Mountains to British Columbia ............................ Sections al and a2.
Section al.
West of western. Montana and southwestern Idaho, and southward to Santa Barbara
County, California ......................................... Species 1, page 81.
South of southern Colorado and Utah, into Texas and Mexico, and westward into
southern California, and possibly in the Coast Range and northward along the forested foothills into northern California ..................... Species 2, page 85.
Section a2.

Southem Colorado and Utah, southward into Mexico ............. Species 3, page 87.
Atlantic and Gulf States, southwestward into Texas.. Species 4, page 90.
Central to southern Arizona .................................. Species 5, page 95.
Southern Mexico .................................. Species 6 and 7, pages 97, 99.
Central Colorado and southern, Utah, southward to southern Arizona, and New Mexico.
Species 8, page 101.
a For exact and probable distribution see maps under description of each species,

78 THE SCOLYTID BEETLES.

SUBDIVISION B.

West of western Montana and southwestern Idaho, south through the Sierra Nevada
Mountains of California................................... Species 9, page 105.
Western South Dakota and southern Wyoming, southward through Utah, Colorado,
to southern Arizona and New Mexico..................... Species 10, page 109.
Northern California, southward in Sierra Nevada, into San Bernardino County, California................................................... Species 11, page 114.

DIVISION II.

SUBDIVISION C.

Maine to western Michigan, southward into northwestern West Virginia.
Species 12, page 117.
Northern Idaho and Montana, south to southern Arizona and New Mexico, and northern Washington, south into Santa Barbara County, California. Species 13, page 121.

Section a4.

Maine to northeastern Minnesota, southward to central Pennsylvania.
Species 14, page 126.
Northern Idaho, east to western South Dakota, southward to southern Arizona and
New Mexico............................................. Species 15, page 130.
Alaska.................................................... Species 16, page 133.
Alaska?, along the coast to northwestern California............ Species 17, page 135.
Lake Superior region........................................ Species 18, page 138.
\Western Montana southeast to central Colorado................ Species 19, page 140.
Higher mountains of New York,Pennsylvania, and WestVirginia. Species 20, page 142. Central Europe to Denmark, Russia, and eastward into Siberia. Species 21, page 143.

SUBDIVISION D.

Atlntic States south of Massachusetts, to Tampa, Florida, westward to western West
Virginia and Texas.................................... Species 22, page 147.
Mountains and foothills of North Carolina, northward into Maine and northwestern
Washington, southward into Guatemala ................. Species 23, page 151.
Guatemala................................................ Species 24, page 157.

Adult (figs. 1, 2, 3).-Antennal funiculus 5-jointed; club broad, thickened at base, compressed toward apex, and usually with 4 distinct segments, the sutures curved or nearly straight; tarsi with joint 3 bilobed; tibia with inner angle produced and armed with a single tooth; outer angle oblique and armed with 3 or more stout teeth; distinct dorsal impression toward apex for the retractile tarsus.

80 THE SCOLYTID BEETLES.

Anterior coxT approximate or subcontiguous. Abdominal sternites with ends of sutures 4, 5, and 6 strongly recurved. Body cylindrical, subelongate to stout, ranging in color from reddish and brown to deep black. Head prominent and large, with distinct epistomal process at anterior margin of front. Eyes transversely placed and oblong-oval to oblong-ovate. Antennal insertion in front of ventral end of eye. Pronotum with sides nearly parallel to narrowed and constricted toward head, one-fourth to one-third broader than long. Elytra with base elevated and rugose, remaining surface rugose, with punctured strim and the declivity convex to subconvex.
Pupa (figs. 37, 38).-The pupa is of the general size of the adult, and is distinguished by its broad prominent head, and the form of the prothorax. The sculpture and armature vary with the age of the specimen. In the preimaginal stage the granules and spines become more obscure.
Larva (text fig. 39; P1. VIII).-The body of a matured larva of a given species is somewhat longer than the adult or pupa, and is cylindrical, deeply wrinkled, legless, and with a few long hairs on each segment, becoming longer on the posterior ones. The head is moderately large, shining, yellowish, and with a few hairs on the scutellar lobes. Front distinct; antenna present, but obscure; eye spots not present. The thoracic segments are larger and more prominent in some species than in others. Abdominal segments 1 to 9 are of about equal width and length; 10 is represented by the anal lobe.
'gg.-Short, oval to oblong-oval, pearly white and shining, and apparently without sculpture and specific characters, except in relative size, corresponding with the size of adult representatives of the

(alleries.I-The primary or egg galleries are excavated in the inner bark and sometimes mark or groove the wood and vary in their course in the bark of the tree from transverse and winding to longitudinal an( straight, and normally are of the single unbranched type.
Distribution (Pl. II).--Eastern continent: Central and northern Europe, from Denmark into Siberia. Western continent: Guatemala, northward through the United States into Alaska and Labrador.
Lost trees.-Pinus, PIicea, Pseudotsuga, Larix, and Abies, the latter rarely if at all.